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1
Fiteha, Yosur G., i Mahmoud Magdy. "The Evolutionary Dynamics of the Mitochondrial tRNA in the Cichlid Fish Family". Biology 11, nr 10 (18.10.2022): 1522. http://dx.doi.org/10.3390/biology11101522.
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The mitochondrial transfer RNA genes (tRNAs) attract more attention due to their highly dynamic and rapidly evolving nature. The current study aimed to detect and evaluate the dynamics, characteristic patterns, and variations of mitochondrial tRNAs. The study was conducted in two main parts: first, the published mitogenomic sequences of cichlids mt tRNAs have been filtered. Second, the filtered mitochondrial tRNA and additional new mitogenomes representing the most prevalent Egyptian tilapiine were compared and analyzed. Our results revealed that all 22 tRNAs of cichlids folded into a classical cloverleaf secondary structure with four domains, except for trnSGCU, missing the D domain in all cichlids. When consensus tRNAs were compared, most of the mutations were observed in the trnP at nucleotide levels (substitutions and indels), in contrast to trnLUAA. From a structural perspective, the anticodon loop and T-loop formations were the most conserved structures among all parts of the tRNA in contrast to the A-stem and D-loop formations. The trnW was the lowest polymorphic unneutral tRNA among all cichlids (both the family and the haplotilapiine lineage), in contrast with the neutral trnD that was extremely polymorphic among and within the haplotilapiine lineage species compared to other cichlids species. From a phylogenetic perspective, the trnC was extremely hypervariable and neutral tRNA in both haplotilapiine lineage and cichlids but was unable to report correct phylogenetic signal for the cichlids. In contrast to trnI and trnY, less variable neutral tRNAs that were able to cluster the haplotilapiine lineage and cichlids species as previously reported. By observing the DNA polymorphism in the coding DNA sequences (CDS), the highest affected amino acid by non-synonymous mutations was isoleucine and was equally mutated to valine and vice versa; no correlation between mutations in CDS and tRNAs was statistically found. The current study provides an insight into the mitochondrial tRNA evolution and its effect on the cichlid diversity and speciation model at the maternal level.
2
Urbonavičius, Jaunius, Jérôme M. B. Durand i Glenn R. Björk. "Three Modifications in the D and T Arms of tRNA Influence Translation in Escherichia coli and Expression of Virulence Genes in Shigella flexneri". Journal of Bacteriology 184, nr 19 (1.10.2002): 5348–57. http://dx.doi.org/10.1128/jb.184.19.5348-5357.2002.
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ABSTRACT The modified nucleosides 2′-O-methylguanosine, present at position 18 (Gm18), 5-methyluridine, present at position 54 (m5U54), and pseudouridine, present at position 55 (Ψ55), are located in the D and T arms of tRNAs and are close in space in the three-dimensional (3D) structure of this molecule in the bacterium Escherichia coli. The formation of these modified nucleosides is catalyzed by the products of genes trmH (Gm18), trmA (m5U54), and truB (Ψ55). The combination of trmH, trmA, and truB mutations resulting in lack of these three modifications reduced the growth rate, especially at high temperature. Moreover, the lack of three modified nucleotides in tRNA induced defects in the translation of certain codons, sensitivity to amino acid analog 3,4-dehydro-dl-proline, and an altered oxidation of some carbon compounds. The results are consistent with the suggestion that these modified nucleosides, two of which directly interact in the 3D structure of tRNA by forming a hydrogen bond between Ψ55 and Gm18, stabilize the structure of the tRNA. Moreover, lack of Ψ55 in tRNA of human pathogen Shigella flexneri leads to a reduced expression of several virulence-associated genes.
3
Mangroo, Dev, Xin-Qi Wu i Uttam L. Rajbhandary. "Escherichia coliinitiator tRNA: structure–function relationships and interactions with the translational machinery". Biochemistry and Cell Biology 73, nr 11-12 (1.12.1995): 1023–31. http://dx.doi.org/10.1139/o95-109.
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We showed previously that the sequence and (or) structural elements important for specifying the many distinctive properties of Escherichia coli initiator tRNA are clustered in the acceptor stem and in the anticodon stem and loop. This paper briefly describes this and reviews the results of some recently published studies on the mutant initiator tRNAs generated during this work. First, we have studied the effect of overproduction of methionyl-tRNA transformylase (MTF) and initiation factors IF2 and IF3 on activity of mutant initiator tRNAs mat are defective at specific steps in the initiation pathway. Overproduction of MTF rescued specifically the activity of mutant tRNAs defective in formylation but not mutants defective in binding to the P site. Overproduction of IF2 increased me activity of all mutant tRNAs having the CUA anticodon but not of mutant tRNA having me GAC anticodon. Overproduction of IF3 had no effect on the activity of any of me mutant tRNAs tested. Second, for functional studies of mutant initiator tRNA in vivo, we used a CAU→CUA anticodon sequence mutant mat can initiate protein synthesis from UAG instead of AUG. In contrast with me wild-type initiator tRNA, the mutant initiator tRNA has a 2-methylthio-N6-isopentenyl adenosine (ms2i6A) base modification next to the anticodon. Interestingly, this base modification is now important for activity of the mutant tRNA in initiation. In a miaA strain of E. coli deficient in biosynthesis of ms2i6A, the mutant initiator tRNA is much less active in initiation. The defect is specifically in binding to the ribosomal P site.Key words: initiator tRNA, initiation Factors, formylation, P site binding, base modification.
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Teramoto, Takamasa, Kipchumba J. Kaitany, Yoshimitsu Kakuta, Makoto Kimura, Carol A. Fierke i Traci M. Tanaka Hall. "Pentatricopeptide repeats of protein-only RNase P use a distinct mode to recognize conserved bases and structural elements of pre-tRNA". Nucleic Acids Research 48, nr 21 (28.07.2020): 11815–26. http://dx.doi.org/10.1093/nar/gkaa627.
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Abstract Pentatricopeptide repeat (PPR) motifs are α-helical structures known for their modular recognition of single-stranded RNA sequences with each motif in a tandem array binding to a single nucleotide. Protein-only RNase P 1 (PRORP1) in Arabidopsis thaliana is an endoribonuclease that uses its PPR domain to recognize precursor tRNAs (pre-tRNAs) as it catalyzes removal of the 5′-leader sequence from pre-tRNAs with its NYN metallonuclease domain. To gain insight into the mechanism by which PRORP1 recognizes tRNA, we determined a crystal structure of the PPR domain in complex with yeast tRNAPhe at 2.85 Å resolution. The PPR domain of PRORP1 bound to the structurally conserved elbow of tRNA and recognized conserved structural features of tRNAs using mechanisms that are different from the established single-stranded RNA recognition mode of PPR motifs. The PRORP1 PPR domain-tRNAPhe structure revealed a conformational change of the PPR domain upon tRNA binding and moreover demonstrated the need for pronounced overall flexibility in the PRORP1 enzyme conformation for substrate recognition and catalysis. The PRORP1 PPR motifs have evolved strategies for protein-tRNA interaction analogous to tRNA recognition by the RNA component of ribonucleoprotein RNase P and other catalytic RNAs, indicating convergence on a common solution for tRNA substrate recognition.
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Chiang, C. C., i A. M. Lambowitz. "The Mauriceville retroplasmid reverse transcriptase initiates cDNA synthesis de novo at the 3' end of tRNAs." Molecular and Cellular Biology 17, nr 8 (sierpień 1997): 4526–35. http://dx.doi.org/10.1128/mcb.17.8.4526.
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The Mauriceville retroplasmid of Neurospora mitochondria encodes a novel reverse transcriptase that initiates cDNA synthesis de novo (i.e., without a primer) at the 3' CCA of the plasmid transcript's 3' tRNA-like structure (H. Wang and A. M. Lambowitz, Cell 75:1071-1081, 1993). Here, we show that the plasmid reverse transcriptase also initiates cDNA synthesis de novo at the 3' end of tRNAs, leading to synthesis of a full-length cDNA copy of the tRNA. The use of tRNA templates in vivo was suggested previously by the structure of suppressive mutant plasmids that have incorporated mitochondrial tRNA sequences (R. A. Akins, R. L. Kelley, and A. M. Lambowitz, Cell 47:505-516, 1986). The in vitro experiments show that efficient de novo initiation on tRNA templates requires an unpaired 3' CCA and occurs predominantly opposite position C-2 of the 3' CCA sequence, the same position as in the plasmid transcript. In other reactions, the plasmid reverse transcriptase synthesizes cDNA dimers by template switching between two tRNA templates and initiates at an internal position in a tRNA by using the 3' end of the tRNA as a primer. Finally, we show that template switching between the tRNA and the plasmid transcript in vitro gives rise to hybrid cDNAs of the type predicted to be intermediates in the generation of the suppressive mutant plasmids. The ability of the plasmid reverse transcriptase to initiate at the 3' end of tRNAs presumably reflects the recognition of structural features similar to those of the 3' tRNA-like structure of the plasmid transcript. The recognition of tRNAs or tRNA-like structures as templates for cDNA synthesis may be characteristic of primitive reverse transcriptases that evolved from RNA-dependent RNA polymerases.
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Nakamura, Akiyoshi, Taiki Nemoto, Isao Tanaka i Min Yao. "Structural analysis of tRNA(His) guanylyltransferase comlexed with tRNA". Acta Crystallographica Section A Foundations and Advances 70, a1 (5.08.2014): C1816. http://dx.doi.org/10.1107/s2053273314081844.
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tRNA(His) guanylyltransferase (Thg1) of eukaryote adds a guanylate to the 5' end of immature or incorrectly processed tRNAs (3'-5' polymerization) by three reaction steps: adenylylation; guanylylation and dephosphorylation. This additional guanylate provides the major identity element for histidyl-tRNA synthetase to recognize its cognate substrate tRNA(His) and differentiates tRNA(His) from the pool of tRNAs present in the cell (1). Previous studies indicate that Thg1 is a structural homolog of canonical 5'-3' polymerases in the catalytic core with no obvious conservation of the amino acid sequence(2). However, the substrate binding of Thg1 is unclear and requires information on the three-dimensional structure in complex with tRNA. In this study, we determined the crystal structures of Thg1 from Candida albicans (CaThg1) in tRNA-bound (CaThg1-tRNA), ATP-bound (CaThg1-ATP), and GTP-bound (CaThg1-GTP) form, and elucidated how Thg1 functions as a reverse polymerase to add nucleotide(3). The crystal structures of CaThg1-tRNA complex shows that two tRNAs are bound to tetrameric Thg1 in parallel orientation which is consistent with SAXS (Small angle X-ray scattering) and gel filtration analysis. One tRNA interacts with three monomers for its positioning, anticodon recognition, and catalytic activation. The end of the acceptor stem and the anticodon loop are both recognized by the same sub-domain belonging to the different monomers. Moreover, the structural comparison of Thg1-tRNA with canonical 5'-3' polymerase shows that the domain architecture of Thg1 is reversed to that of canonical 5'-3' polymerase.
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Hòa, Lê Thanh, Nguyễn Thị Khuê, Nguyễn Thị Bích Nga, Đỗ Thị Roan, Đỗ Trung Dũng, Lê Thị Kim Xuyến i Đoàn Thị Thanh Hương. "Genetic characterization of mitochondrial genome of the small intestinal fluke, Haplorchis taichui (Trematoda: Heterophyidae), Vietnamese sample". Vietnam Journal of Biotechnology 14, nr 2 (30.06.2016): 215–24. http://dx.doi.org/10.15625/1811-4989/14/2/9333.
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The small intestinal fluke, Haplorchis taichui Nishigori, 1924, belonging to genus Haplorchis (family Heterophyidae, class Trematoda, phylum Platyhelminthes), is a zoonotic pathogen causing disease in humans and animals. Complete mitochondrial genome (mtDNA) of H. taichui (strain HTAQT, collected from Quang Tri) was obtained and characterized for structural genomics providing valuable data for studies on epidemiology, species identification, diagnosis, classification, molecular phylogenetic relationships and prevention of the disease. The entire nucleotide mtDNA sequence of H. taichui (HTAQT) is 15.119 bp in length, containing 36 genes, including 12 protein-coding genes (cox1, cox2, cox3, nad1, nad2, nad3, nad4L, nad4, nad5, nad6, atp6 and cob); 2 ribosomal RNA genes, rrnL (16S) and rrnS (12S); 22 transfer RNA genes (tRNA or trn), and a non-coding region (NR), divided into two sub-regions of short non-coding (short, SNR) and long non-coding (long, LNR). LNR region, 1.692 bp in length, located between the position of trnG (transfer RNA-Glycine) and trnE (Glutamic acid), contains 6 tandem repeats (TR), arranged as TR1A, TR2A, TR1B, TR2B, TR3A, TR3B, respectively. Each protein coding gene (overall, 12 genes), ribosomal rRNA (2 genes) and tRNA (22 genes) were analyzed, in particular, protein-coding genes were defined in length, start and stop codons, and rRNA and tRNA genes for secondary structure.
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Ramos-Morales, Elizabeth, Efil Bayam, Jordi Del-Pozo-Rodríguez, Thalia Salinas-Giegé, Martin Marek, Peggy Tilly, Philippe Wolff i in. "The structure of the mouse ADAT2/ADAT3 complex reveals the molecular basis for mammalian tRNA wobble adenosine-to-inosine deamination". Nucleic Acids Research 49, nr 11 (31.05.2021): 6529–48. http://dx.doi.org/10.1093/nar/gkab436.
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Abstract Post-transcriptional modification of tRNA wobble adenosine into inosine is crucial for decoding multiple mRNA codons by a single tRNA. The eukaryotic wobble adenosine-to-inosine modification is catalysed by the ADAT (ADAT2/ADAT3) complex that modifies up to eight tRNAs, requiring a full tRNA for activity. Yet, ADAT catalytic mechanism and its implication in neurodevelopmental disorders remain poorly understood. Here, we have characterized mouse ADAT and provide the molecular basis for tRNAs deamination by ADAT2 as well as ADAT3 inactivation by loss of catalytic and tRNA-binding determinants. We show that tRNA binding and deamination can vary depending on the cognate tRNA but absolutely rely on the eukaryote-specific ADAT3 N-terminal domain. This domain can rotate with respect to the ADAT catalytic domain to present and position the tRNA anticodon-stem-loop correctly in ADAT2 active site. A founder mutation in the ADAT3 N-terminal domain, which causes intellectual disability, does not affect tRNA binding despite the structural changes it induces but most likely hinders optimal presentation of the tRNA anticodon-stem-loop to ADAT2.
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O'Donoghue, Patrick, i Zaida Luthey-Schulten. "On the Evolution of Structure in Aminoacyl-tRNA Synthetases". Microbiology and Molecular Biology Reviews 67, nr 4 (grudzień 2003): 550–73. http://dx.doi.org/10.1128/mmbr.67.4.550-573.2003.
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SUMMARY The aminoacyl-tRNA synthetases are one of the major protein components in the translation machinery. These essential proteins are found in all forms of life and are responsible for charging their cognate tRNAs with the correct amino acid. The evolution of the tRNA synthetases is of fundamental importance with respect to the nature of the biological cell and the transition from an RNA world to the modern world dominated by protein-enzymes. We present a structure-based phylogeny of the aminoacyl-tRNA synthetases. By using structural alignments of all of the aminoacyl-tRNA synthetases of known structure in combination with a new measure of structural homology, we have reconstructed the evolutionary history of these proteins. In order to derive unbiased statistics from the structural alignments, we introduce a multidimensional QR factorization which produces a nonredundant set of structures. Since protein structure is more highly conserved than protein sequence, this study has allowed us to glimpse the evolution of protein structure that predates the root of the universal phylogenetic tree. The extensive sequence-based phylogenetic analysis of the tRNA synthetases (Woese et al., Microbiol. Mol. Biol. Rev. 64:202-236, 2000) has further enabled us to reconstruct the complete evolutionary profile of these proteins and to make connections between major evolutionary events and the resulting changes in protein shape. We also discuss the effect of functional specificity on protein shape over the complex evolutionary course of the tRNA synthetases.
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Strobel, M. C., i J. Abelson. "Effect of intron mutations on processing and function of Saccharomyces cerevisiae SUP53 tRNA in vitro and in vivo". Molecular and Cellular Biology 6, nr 7 (lipiec 1986): 2663–73. http://dx.doi.org/10.1128/mcb.6.7.2663-2673.1986.
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The Saccharomyces cerevisiae leucine-inserting amber suppressor tRNA gene SUP53 (a tRNALeu3 allele) was used to investigate the relationship between precursor tRNA structure and mature tRNA function. This gene encodes a pre-tRNA which contains a 32-base intron. The mature tRNASUP53 contains a 5-methylcytosine modification of the anticodon wobble base. Mutations were made in the SUP53 intron. These mutant genes were transcribed in an S. cerevisiae nuclear extract preparation. In this extract, primary tRNA gene transcripts are end-processed and base modified after addition of cofactors. The base modifications made in vitro were examined, and the mutant pre-tRNAs were analyzed for their ability to serve as substrates for partially purified S. cerevisiae tRNA endonuclease and ligase. Finally, the suppressor function of these mutant tRNA genes was assayed after their integration into the S. cerevisiae genome. Mutant analysis showed that the totally intact precursor tRNA, rather than any specific sequence or structure of the intron, was necessary for efficient nonsense suppression by tRNASUP53. Less efficient suppressor activity correlated with the absence of the 5-methylcytosine modification. Most of the intron-altered precursor tRNAs were successfully spliced in vitro, indicating that modifications are not critical for recognition by the tRNA endonuclease and ligase.
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Strobel, M. C., i J. Abelson. "Effect of intron mutations on processing and function of Saccharomyces cerevisiae SUP53 tRNA in vitro and in vivo." Molecular and Cellular Biology 6, nr 7 (lipiec 1986): 2663–73. http://dx.doi.org/10.1128/mcb.6.7.2663.
Pełny tekst źródłaStreszczenie:
The Saccharomyces cerevisiae leucine-inserting amber suppressor tRNA gene SUP53 (a tRNALeu3 allele) was used to investigate the relationship between precursor tRNA structure and mature tRNA function. This gene encodes a pre-tRNA which contains a 32-base intron. The mature tRNASUP53 contains a 5-methylcytosine modification of the anticodon wobble base. Mutations were made in the SUP53 intron. These mutant genes were transcribed in an S. cerevisiae nuclear extract preparation. In this extract, primary tRNA gene transcripts are end-processed and base modified after addition of cofactors. The base modifications made in vitro were examined, and the mutant pre-tRNAs were analyzed for their ability to serve as substrates for partially purified S. cerevisiae tRNA endonuclease and ligase. Finally, the suppressor function of these mutant tRNA genes was assayed after their integration into the S. cerevisiae genome. Mutant analysis showed that the totally intact precursor tRNA, rather than any specific sequence or structure of the intron, was necessary for efficient nonsense suppression by tRNASUP53. Less efficient suppressor activity correlated with the absence of the 5-methylcytosine modification. Most of the intron-altered precursor tRNAs were successfully spliced in vitro, indicating that modifications are not critical for recognition by the tRNA endonuclease and ligase.
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BYKHOVSKI, ALEXEI, TATIANA GLOBUS, TATYANA KHROMOVA, BORIS GELMONT i DWIGHT WOOLARD. "AN ANALYSIS OF THE THZ FREQUENCY SIGNATURES IN THE CELLULAR COMPONENTS OF BIOLOGICAL AGENTS". International Journal of High Speed Electronics and Systems 17, nr 02 (czerwiec 2007): 225–37. http://dx.doi.org/10.1142/s012915640700445x.
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The development of an effective biological (bio) agent detection capability based upon terahertz (THz) frequency absorption spectra will require insight into how the constituent cellular components contribute to the overall THz signature. In this work, the specific contribution of ribonucleic acid (RNA) to THz spectra is analyzed in detail. Previously, it has only been possible to simulate partial fragments of the RNA (or DNA) structures due to the excessive computational demands. For the first time, the molecular structure of the entire transfer RNA (tRNA) molecule of E. coli was simulated and the associated THz signature was derived theoretically. The tRNA that binds amino acid tyrosine (tRNAtyr) was studied. Here, the molecular structure was optimized using the potential energy minimization and molecular dynamical (MD) simulations. Solvation effects (water molecules) were also included explicitly in the MD simulations. To verify that realistic molecular signatures were simulated, a parallel experimental study of tRNAs of E. coli was also conducted. Two very similar molecules, valine and tyrosine tRNA were investigated experimentally. Samples were prepared in the form of water solutions with the concentrations in the range 0.01-1 mg/ml. A strong correlation of the measured THz signatures associated with valine tRNA and tyrosine tRNA was observed. These findings are consistent with the structural similarity of the two tRNAs. The calculated THz signature of the tyrosine tRNA of E. coli reproduces many features of our measured spectra, and, therefore, provides valuable new insights into bio-agent detection.
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Kawabata, Mai, Kentaro Kawashima, Hiromi Mutsuro-Aoki, Tadashi Ando, Takuya Umehara i Koji Tamura. "Peptide Bond Formation between Aminoacyl-Minihelices by a Scaffold Derived from the Peptidyl Transferase Center". Life 12, nr 4 (12.04.2022): 573. http://dx.doi.org/10.3390/life12040573.
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The peptidyl transferase center (PTC) in the ribosome is composed of two symmetrically arranged tRNA-like units that contribute to peptide bond formation. We prepared units of the PTC components with putative tRNA-like structure and attempted to obtain peptide bond formation between aminoacyl-minihelices (primordial tRNAs, the structures composed of a coaxial stack of the acceptor stem on the T-stem of tRNA). One of the components of the PTC, P1c2UGGU (74-mer), formed a dimer and a peptide bond was formed between two aminoacyl-minihelices tethered by the dimeric P1c2UGGU. Peptide synthesis depended on both the existence of the dimeric P1c2UGGU and the sequence complementarity between the ACCA-3′ sequence of the minihelix. Thus, the tRNA-like structures derived from the PTC could have originated as a scaffold of aminoacyl-minihelices for peptide bond formation through an interaction of the CCA sequence of minihelices. Moreover, with the same origin, some would have evolved to constitute the present PTC of the ribosome, and others to function as present tRNAs.
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Cummins, C. M., M. R. Culbertson i G. Knapp. "Frameshift suppressor mutations outside the anticodon in yeast proline tRNAs containing an intervening sequence". Molecular and Cellular Biology 5, nr 7 (lipiec 1985): 1760–71. http://dx.doi.org/10.1128/mcb.5.7.1760-1771.1985.
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Extragenic suppressors of +1 frameshift mutations in proline codons map in genes encoding two major proline tRNA isoacceptors. We have shown previously that one isoacceptor encoded by the SUF2 gene (chromosome 3) contains no intervening sequence. SUF2 suppressor mutations result from the base insertion of a G within a 3'-GGA-5' anticodon, allowing the tRNA to read a 4-base code word. In this communication we describe suppressor mutations in genes encoding a second proline tRNA isoacceptor (wild-type anticodon 3'-GGU-5') that result in a novel mechanism for translation of a 4-base genetic code word. The genes that encode this isoacceptor include SUF7 (chromosome 13), SUF8 (chromosome 8), trn1 (chromosome 1), and at least two additional unmapped genes, all of which contain an intervening sequence. We show that suppressor mutations in the SUF7 and SUF8 genes result in G-to-U base substitutions at position 39 that disrupted the normal G . C base pairing in the last base pair of the anticodon stem adjacent to the anticodon loop. These anticodon stem mutations might alter the size of the anticodon loop and permit the use of a 3'-GGGU-5' sequence within the loop to read 4-base proline codons. Uncertainty regarding the exact structure of the mature suppressor tRNAs results from the possibility that anticodon stem mutations might affect sites of intervening sequence removal. The possible role of the intervening sequence in the generation of mature suppressor tRNA is discussed. Besides an analysis of suppressor tRNA genes, we have extended previous observations of the apparent relationship between tRNA genes and repetitive delta sequences found as solo elements or in association with the transposable element TY1. Hybridization studies and a computer analysis of the DNA sequence surrounding the SUF7 gene revealed two incomplete, inverted delta sequences that form a stem and loop structure located 165 base pairs from the 5' end of the tRNA gene. In addition, sequences beginning 164 base pairs from the 5' end of the trn1 gene also exhibit partial homology to delta. These observations provide further evidence for a nonrandom association between tRNA genes and delta sequences.
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Cummins, C. M., M. R. Culbertson i G. Knapp. "Frameshift suppressor mutations outside the anticodon in yeast proline tRNAs containing an intervening sequence." Molecular and Cellular Biology 5, nr 7 (lipiec 1985): 1760–71. http://dx.doi.org/10.1128/mcb.5.7.1760.
Pełny tekst źródłaStreszczenie:
Extragenic suppressors of +1 frameshift mutations in proline codons map in genes encoding two major proline tRNA isoacceptors. We have shown previously that one isoacceptor encoded by the SUF2 gene (chromosome 3) contains no intervening sequence. SUF2 suppressor mutations result from the base insertion of a G within a 3'-GGA-5' anticodon, allowing the tRNA to read a 4-base code word. In this communication we describe suppressor mutations in genes encoding a second proline tRNA isoacceptor (wild-type anticodon 3'-GGU-5') that result in a novel mechanism for translation of a 4-base genetic code word. The genes that encode this isoacceptor include SUF7 (chromosome 13), SUF8 (chromosome 8), trn1 (chromosome 1), and at least two additional unmapped genes, all of which contain an intervening sequence. We show that suppressor mutations in the SUF7 and SUF8 genes result in G-to-U base substitutions at position 39 that disrupted the normal G . C base pairing in the last base pair of the anticodon stem adjacent to the anticodon loop. These anticodon stem mutations might alter the size of the anticodon loop and permit the use of a 3'-GGGU-5' sequence within the loop to read 4-base proline codons. Uncertainty regarding the exact structure of the mature suppressor tRNAs results from the possibility that anticodon stem mutations might affect sites of intervening sequence removal. The possible role of the intervening sequence in the generation of mature suppressor tRNA is discussed. Besides an analysis of suppressor tRNA genes, we have extended previous observations of the apparent relationship between tRNA genes and repetitive delta sequences found as solo elements or in association with the transposable element TY1. Hybridization studies and a computer analysis of the DNA sequence surrounding the SUF7 gene revealed two incomplete, inverted delta sequences that form a stem and loop structure located 165 base pairs from the 5' end of the tRNA gene. In addition, sequences beginning 164 base pairs from the 5' end of the trn1 gene also exhibit partial homology to delta. These observations provide further evidence for a nonrandom association between tRNA genes and delta sequences.
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Wang, S. S., i A. K. Hopper. "Isolation of a yeast gene involved in species-specific pre-tRNA processing". Molecular and Cellular Biology 8, nr 12 (grudzień 1988): 5140–49. http://dx.doi.org/10.1128/mcb.8.12.5140-5149.1988.
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To identify genes involved in pre-tRNA processing, we searched for yeast DNA sequences that specifically enhanced the expression of the SUP4(G37) gene. The SUP4(G37) gene possesses a point mutation at position 37 of suppressor tRNA(Tyr). This lesion results in a reduced rate of pre-tRNA splicing and a decreased level of nonsense suppression. A SUP4(G37) strain was transformed with a yeast genomic library, and the transformants were screened for increased suppressor activity. One transformant contained a plasmid that encoded an unessential gene, STP1, that in multiple copies enhanced the suppression of SUP4(G37) and caused increased production of mature SUP4(G37) product. Disruption of the genomic copy of STP1 resulted in a reduced efficiency of SUP4-mediated suppression and the accumulation of pre-tRNAs. Not all intron-containing pre-tRNAs were affected by the stp1-disruption. At least five of the nine families of pre-tRNAs were affected. Two other species, pre-tRNA(Ile) and pre-tRNA(3Leu), were not. We propose that STP1 encodes a tRNA species-specific product that functions as a helper for pre-tRNA splicing. The STP1 product may interact with pre-tRNAs to generate a structure that is efficiently recognized by splicing machinery.
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Wang, S. S., i A. K. Hopper. "Isolation of a yeast gene involved in species-specific pre-tRNA processing." Molecular and Cellular Biology 8, nr 12 (grudzień 1988): 5140–49. http://dx.doi.org/10.1128/mcb.8.12.5140.
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To identify genes involved in pre-tRNA processing, we searched for yeast DNA sequences that specifically enhanced the expression of the SUP4(G37) gene. The SUP4(G37) gene possesses a point mutation at position 37 of suppressor tRNA(Tyr). This lesion results in a reduced rate of pre-tRNA splicing and a decreased level of nonsense suppression. A SUP4(G37) strain was transformed with a yeast genomic library, and the transformants were screened for increased suppressor activity. One transformant contained a plasmid that encoded an unessential gene, STP1, that in multiple copies enhanced the suppression of SUP4(G37) and caused increased production of mature SUP4(G37) product. Disruption of the genomic copy of STP1 resulted in a reduced efficiency of SUP4-mediated suppression and the accumulation of pre-tRNAs. Not all intron-containing pre-tRNAs were affected by the stp1-disruption. At least five of the nine families of pre-tRNAs were affected. Two other species, pre-tRNA(Ile) and pre-tRNA(3Leu), were not. We propose that STP1 encodes a tRNA species-specific product that functions as a helper for pre-tRNA splicing. The STP1 product may interact with pre-tRNAs to generate a structure that is efficiently recognized by splicing machinery.
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Caulfield, Thomas R., Batsal Devkota i Geoffrey C. Rollins. "Examinations of tRNA Range of Motion Using Simulations of Cryo-EM Microscopy and X-Ray Data". Journal of Biophysics 2011 (28.03.2011): 1–11. http://dx.doi.org/10.1155/2011/219515.
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We examined tRNA flexibility using a combination of steered and unbiased molecular dynamics simulations. Using Maxwell's demon algorithm, molecular dynamics was used to steer X-ray structure data toward that from an alternative state obtained from cryogenic-electron microscopy density maps. Thus, we were able to fit X-ray structures of tRNA onto cryogenic-electron microscopy density maps for hybrid states of tRNA. Additionally, we employed both Maxwell's demon molecular dynamics simulations and unbiased simulation methods to identify possible ribosome-tRNA contact areas where the ribosome may discriminate tRNAs during translation. Herein, we collected >500 ns of simulation data to assess the global range of motion for tRNAs. Biased simulations can be used to steer between known conformational stop points, while unbiased simulations allow for a general testing of conformational space previously unexplored. The unbiased molecular dynamics data describes the global conformational changes of tRNA on a sub-microsecond time scale for comparison with steered data. Additionally, the unbiased molecular dynamics data was used to identify putative contacts between tRNA and the ribosome during the accommodation step of translation. We found that the primary contact regions were H71 and H92 of the 50S subunit and ribosomal proteins L14 and L16.
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Akins, R. A., R. L. Kelley i A. M. Lambowitz. "Characterization of mutant mitochondrial plasmids of Neurospora spp. that have incorporated tRNAs by reverse transcription". Molecular and Cellular Biology 9, nr 2 (luty 1989): 678–91. http://dx.doi.org/10.1128/mcb.9.2.678-691.1989.
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The Mauriceville and Varkud mitochondrial plasmids of Neurospora spp. are closely related, closed-circular DNAs (3.6 and 3.7 kilobases, respectively) whose nucleotide sequences and genetic organization suggest relationships to mitochondrial introns and retroelements. We have characterized nine suppressive mutants of these plasmids that outcompete mitochondrial DNA and lead to impaired growth. All nine suppressive plasmids contain small insertions, corresponding to or including a mitochondrial tRNA (tRNATrp, tRNAGly, or tRNAVal) or a tRNA-like sequence. The insertions are located at the position corresponding to the 5' end of the major plasmid transcript or 24 nucleotides downstream near a cognate of the sequence at the major 5' RNA end. The structure of the suppressive plasmids suggests that the tRNAs were inserted via an RNA intermediate. The 3' end of the wild-type plasmid transcript can itself be folded into a secondary structure which has tRNA-like characteristics, similar to the tRNA-like structures at the 3' ends of plant viral RNAs. This structure may play a role in replication of the plasmids by reverse transcription. Major transcripts of the suppressive plasmids begin at the 5' end of the inserted mitochondrial tRNA sequence and are present in 25- to 100-fold-higher concentrations than are transcripts of wild-type plasmids. Mapping of 5' RNA ends within the inserted mtDNA sequences identifies a short consensus sequence (PuNPuAG) which is present at the 5' ends of a subset of mitochondrial tRNA genes. This sequence, together with sequences immediately upstream in the plasmids, forms a longer consensus sequence, which is similar to sequences at transcription initiation sites in Neurospora mitochondrial DNA. The suppressive behavior of the plasmids is likely to be directly related to the insertion of tRNAs leading to overproduction of plasmid transcripts.
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Akins, R. A., R. L. Kelley i A. M. Lambowitz. "Characterization of mutant mitochondrial plasmids of Neurospora spp. that have incorporated tRNAs by reverse transcription." Molecular and Cellular Biology 9, nr 2 (luty 1989): 678–91. http://dx.doi.org/10.1128/mcb.9.2.678.
Pełny tekst źródłaStreszczenie:
The Mauriceville and Varkud mitochondrial plasmids of Neurospora spp. are closely related, closed-circular DNAs (3.6 and 3.7 kilobases, respectively) whose nucleotide sequences and genetic organization suggest relationships to mitochondrial introns and retroelements. We have characterized nine suppressive mutants of these plasmids that outcompete mitochondrial DNA and lead to impaired growth. All nine suppressive plasmids contain small insertions, corresponding to or including a mitochondrial tRNA (tRNATrp, tRNAGly, or tRNAVal) or a tRNA-like sequence. The insertions are located at the position corresponding to the 5' end of the major plasmid transcript or 24 nucleotides downstream near a cognate of the sequence at the major 5' RNA end. The structure of the suppressive plasmids suggests that the tRNAs were inserted via an RNA intermediate. The 3' end of the wild-type plasmid transcript can itself be folded into a secondary structure which has tRNA-like characteristics, similar to the tRNA-like structures at the 3' ends of plant viral RNAs. This structure may play a role in replication of the plasmids by reverse transcription. Major transcripts of the suppressive plasmids begin at the 5' end of the inserted mitochondrial tRNA sequence and are present in 25- to 100-fold-higher concentrations than are transcripts of wild-type plasmids. Mapping of 5' RNA ends within the inserted mtDNA sequences identifies a short consensus sequence (PuNPuAG) which is present at the 5' ends of a subset of mitochondrial tRNA genes. This sequence, together with sequences immediately upstream in the plasmids, forms a longer consensus sequence, which is similar to sequences at transcription initiation sites in Neurospora mitochondrial DNA. The suppressive behavior of the plasmids is likely to be directly related to the insertion of tRNAs leading to overproduction of plasmid transcripts.
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Qi, Fangbing, Yajing Zhao, Ningbo Zhao, Kai Wang, Zhonghu Li i Yingjuan Wang. "Structural variation and evolution of chloroplast tRNAs in green algae". PeerJ 9 (1.06.2021): e11524. http://dx.doi.org/10.7717/peerj.11524.
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As one of the important groups of the core Chlorophyta (Green algae), Chlorophyceae plays an important role in the evolution of plants. As a carrier of amino acids, tRNA plays an indispensable role in life activities. However, the structural variation of chloroplast tRNA and its evolutionary characteristics in Chlorophyta species have not been well studied. In this study, we analyzed the chloroplast genome tRNAs of 14 species in five categories in the green algae. We found that the number of chloroplasts tRNAs of Chlorophyceae is maintained between 28–32, and the length of the gene sequence ranges from 71 nt to 91 nt. There are 23–27 anticodon types of tRNAs, and some tRNAs have missing anticodons that are compensated for by other types of anticodons of that tRNA. In addition, three tRNAs were found to contain introns in the anti-codon loop of the tRNA, but the analysis scored poorly and it is presumed that these introns are not functional. After multiple sequence alignment, the Ψ-loop is the most conserved structural unit in the tRNA secondary structure, containing mostly U-U-C-x-A-x-U conserved sequences. The number of transitions in tRNA is higher than the number of transversions. In the replication loss analysis, it was found that green algal chloroplast tRNAs may have undergone substantial gene loss during the course of evolution. Based on the constructed phylogenetic tree, mutations were found to accompany the evolution of the Green algae chloroplast tRNA. Moreover, chloroplast tRNAs of Chlorophyceae are consistent with those of monocotyledons and gymnosperms in terms of evolutionary patterns, sharing a common multi-phylogenetic pattern and rooted in a rich common ancestor. Sequence alignment and systematic analysis of tRNA in chloroplast genome of Chlorophyceae, clarified the characteristics and rules of tRNA changes, which will promote the evolutionary relationship of tRNA and the origin and evolution of chloroplast.
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Kelly, Nathan J., i Casey D. Morrow. "Structural Elements of the tRNA TΨC Loop Critical for Nucleocytoplasmic Transport Are Important for Human Immunodeficiency Virus Type 1 Primer Selection". Journal of Virology 79, nr 10 (15.05.2005): 6532–39. http://dx.doi.org/10.1128/jvi.79.10.6532-6539.2005.
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ABSTRACT Human immunodeficiency virus type 1 (HIV-1) selects a host cell tRNA as the primer for the initiation of reverse transcription. In a previous study, transport of the intact tRNA from the nucleus to the cytoplasm during tRNA biogenesis was shown to be a requirement for the selection of the tRNA primer by HIV-1. To further examine the importance of tRNA structure for transport and the selection of the primer, yeast tRNAPhe mutants were designed such that the native tRNA structure would be disrupted to various extents. The capacity of the mutant tRNAPhe to complement a defective HIV-1 provirus that relies on the expression of yeast tRNAPhe for infectivity was determined. We found a direct relationship between intact tRNA conformation and the capacity to be selected by HIV-1 for use in reverse transcription. tRNAPhe mutants that retained the capacity for nucleocytoplasmic transport, indicative of overall intact conformation, complemented the defective provirus. The mutant tRNAs were not aminoacylated, and the levels of complementation were lower than that for wild-type tRNAPhe, which did undergo transport and aminoacylation. Taken together, these results demonstrate that HIV-1 primer selection is most dependent on a tRNA structure necessary for nucleocytoplasmic transport, consistent with primer selection occurring in the cytoplasm at or near the site of protein synthesis.
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Florentz, Catherine. "Molecular Investigations on tRNAs Involved in Human Mitochondrial Disorders". Bioscience Reports 22, nr 1 (1.02.2002): 81–98. http://dx.doi.org/10.1023/a:1016065107165.
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Over the last decade, human neurodegenerative disorders which correlate with point mutations in mitochondrial tRNA genes became more and more numerous. Both the number of mutations (more than 70) and the variety of phenotypes (cardiopathies, myopathies, encephalopathies as well as diabetes, deafness or others) render the understanding of the genotype/phenotype relationships very complex. Here we first summarize the efforts undertaken to decipher the initial impact of various mutations on the structure/function relationships of tRNAs. This includes several lines of research, namely (i) investigation of human mitochrondrial tRNA structures, (ii) comparison of disease-related and polymorphic mutations at a theoretical level, and (iii) experimental investigations of affected tRNAs in the frame of mitochondrial protein synthesis. A new approach aimed at searching for long-range effects of mitochondrial tRNA mutations on a broader global mitochondrial level will also be presented. Initial results obtained by comparative mitochondrial proteomics turn out to be very promising for deciphering unexpected molecular partners involved in the pathological status of the mitochondria.
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Lin, Brian Y., Patricia P. Chan i Todd M. Lowe. "tRNAviz: explore and visualize tRNA sequence features". Nucleic Acids Research 47, W1 (25.05.2019): W542—W547. http://dx.doi.org/10.1093/nar/gkz438.
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Abstract Transfer RNAs (tRNAs) are ubiquitous across the tree of life. Although tRNA structure is highly conserved, there is still significant variation in sequence features between clades, isotypes and even isodecoders. This variation not only impacts translation, but as shown by a variety of recent studies, nontranslation-associated functions are also sensitive to small changes in tRNA sequence. Despite the rapidly growing number of sequenced genomes, there is a lack of tools for both small- and large-scale comparative genomics analysis of tRNA sequence features. Here, we have integrated over 150 000 tRNAs spanning all domains of life into tRNAviz, a web application for exploring and visualizing tRNA sequence features. tRNAviz implements a framework for determining consensus sequence features and can generate sequence feature distributions by isotypes, clades and anticodons, among other tRNA properties such as score. All visualizations are interactive and exportable. The web server is publicly available at http://trna.ucsc.edu/tRNAviz/.
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Ito, Takuhiro, Noriko Kiyasu, Risa Matsunaga, Seizo Takahashi i Shigeyuki Yokoyama. "Structure of nondiscriminating glutamyl-tRNA synthetase fromThermotoga maritima". Acta Crystallographica Section D Biological Crystallography 66, nr 7 (19.06.2010): 813–20. http://dx.doi.org/10.1107/s0907444910019086.
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Aminoacyl-tRNA synthetases produce aminoacyl-tRNAs from the substrate tRNA and its cognate amino acid with the aid of ATP. Two types of glutamyl-tRNA synthetase (GluRS) have been discovered: discriminating GluRS (D-GluRS) and nondiscriminating GluRS (ND-GluRS). D-GluRS glutamylates tRNAGluonly, while ND-GluRS glutamylates both tRNAGluand tRNAGln. ND-GluRS produces the intermediate Glu-tRNAGln, which is converted to Gln-tRNAGlnby Glu-tRNAGlnamidotransferase. Two GluRS homologues fromThermotoga maritima, TM1875 and TM1351, have been biochemically characterized and it has been clarified that only TM1875 functions as an ND-GluRS. Furthermore, the crystal structure of theT. maritimaND-GluRS, TM1875, was determined in complex with a Glu-AMP analogue at 2.0 Å resolution. TheT. maritimaND-GluRS contains a characteristic structure in the connective-peptide domain, which is inserted into the catalytic Rossmann-fold domain. The glutamylation ability of tRNAGlnby ND-GluRS was measured in the presence of the bacterial Glu-tRNAGlnamidotransferase GatCAB. Interestingly, the glutamylation efficiency was not affected even in the presence of excess GatCAB. Therefore, GluRS avoids competition with GatCAB and glutamylates tRNAGln.
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Ito, Takuhiro, Isao Masuda, Ken-ichi Yoshida, Sakurako Goto-Ito, Shun-ichi Sekine, Se Won Suh, Ya-Ming Hou i Shigeyuki Yokoyama. "Structural basis for methyl-donor–dependent and sequence-specific binding to tRNA substrates by knotted methyltransferase TrmD". Proceedings of the National Academy of Sciences 112, nr 31 (16.07.2015): E4197—E4205. http://dx.doi.org/10.1073/pnas.1422981112.
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The deep trefoil knot architecture is unique to the SpoU and tRNA methyltransferase D (TrmD) (SPOUT) family of methyltransferases (MTases) in all three domains of life. In bacteria, TrmD catalyzes the N1-methylguanosine (m1G) modification at position 37 in transfer RNAs (tRNAs) with the 36GG37 sequence, using S-adenosyl-l-methionine (AdoMet) as the methyl donor. The m1G37-modified tRNA functions properly to prevent +1 frameshift errors on the ribosome. Here we report the crystal structure of the TrmD homodimer in complex with a substrate tRNA and an AdoMet analog. Our structural analysis revealed the mechanism by which TrmD binds the substrate tRNA in an AdoMet-dependent manner. The trefoil-knot center, which is structurally conserved among SPOUT MTases, accommodates the adenosine moiety of AdoMet by loosening/retightening of the knot. The TrmD-specific regions surrounding the trefoil knot recognize the methionine moiety of AdoMet, and thereby establish the entire TrmD structure for global interactions with tRNA and sequential and specific accommodations of G37 and G36, resulting in the synthesis of m1G37-tRNA.
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Grigg, Jason C., Ian R. Price i Ailong Ke. "tRNA Fusion to Streamline RNA Structure Determination: Case Studies in Probing Aminoacyl-tRNA Sensing Mechanisms by the T-Box Riboswitch". Crystals 12, nr 5 (13.05.2022): 694. http://dx.doi.org/10.3390/cryst12050694.
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RNAs are prone to misfolding and are often more challenging to crystallize and phase than proteins. Here, we demonstrate that tRNA fusion can streamline the crystallization and structure determination of target RNA molecules. This strategy was applied to the T-box riboswitch system to capture a dynamic interaction between the tRNA 3′-UCCA tail and the T-box antiterminator, which senses aminoacylation. We fused the T-box antiterminator domain to the tRNA anticodon arm to capture the intended interaction through crystal packing. This approach drastically improved the probability of crystallization and successful phasing. Multiple structure snapshots captured the antiterminator loop in an open conformation with some resemblance to that observed in the recent co-crystal structures of the full-length T box riboswitch–tRNA complex, which contrasts the resting, closed conformation antiterminator observed in an earlier NMR study. The anticipated tRNA acceptor–antiterminator interaction was captured in a low-resolution crystal structure. These structures combined with our previous success using prohead RNA–tRNA fusions demonstrates tRNA fusion is a powerful method in RNA structure determination.
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Ding, Yu, Beibei Gao i Jinyu Huang. "Mitochondrial Cardiomyopathy: The Roles of mt-tRNA Mutations". Journal of Clinical Medicine 11, nr 21 (30.10.2022): 6431. http://dx.doi.org/10.3390/jcm11216431.
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Mitochondria are important organelles whose primary role is generating energy through the oxidative phosphorylation (OXPHOS) system. Cardiomyopathy, a common clinical disorder, is frequently associated with pathogenic mutations in nuclear and mitochondrial genes. To date, a growing number of nuclear gene mutations have been linked with cardiomyopathy; however, knowledge about mitochondrial tRNAs (mt-tRNAs) mutations in this disease remain inadequately understood. In fact, defects in mt-tRNA metabolism caused by pathogenic mutations may influence the functioning of the OXPHOS complexes, thereby impairing mitochondrial translation, which plays a critical role in the predisposition of this disease. In this review, we summarize some basic knowledge about tRNA biology, including its structure and function relations, modification, CCA-addition, and tRNA import into mitochondria. Furthermore, a variety of molecular mechanisms underlying tRNA mutations that cause mitochondrial dysfunctions are also discussed in this article.
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McGuire, Andrew T., Robert A. B. Keates, Stephanie Cook i Dev Mangroo. "Structural modeling identified the tRNA-binding domain of Utp8p, an essential nucleolar component of the nuclear tRNA export machinery of Saccharomyces cerevisiae". Biochemistry and Cell Biology 87, nr 2 (kwiecień 2009): 431–43. http://dx.doi.org/10.1139/o08-145.
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Utp8p is an essential 80 kDa intranuclear tRNA chaperone that transports tRNAs from the nucleolus to the nuclear tRNA export receptors in Saccharomyces cerevisiae . To help understand the mechanism of Utp8p function, predictive tools were used to derive a partial model of the tertiary structure of Utp8p. Secondary structure prediction, supported by circular dichroism measurements, indicated that Utp8p is divided into 2 domains: the N-terminal beta sheet and the C-terminal alpha helical domain. Tertiary structure prediction was more challenging, because the amino acid sequence of Utp8p is not directly homologous to any known protein structure. The tertiary structures predicted by threading and fold recognition had generally modest scores, but for the C-terminal domain, threading and fold recognition consistently pointed to an alpha–alpha superhelix. Because of the sequence diversity of this fold type, no single structural template was an ideal fit to the Utp8p sequence. Instead, a composite template was constructed from 3 different alpha–alpha superhelix structures that gave the best matches to different portions of the C-terminal domain sequence. In the resulting model, the most conserved sequences grouped in a tight cluster of positive charges on a protein that is otherwise predominantly negative, suggesting that the positive-charge cleft may be the tRNA-binding site. Mutations of conserved positive residues in the proposed binding site resulted in a reduction in the affinity of Utp8p for tRNA both in vivo and in vitro. Models were also derived for the 10 fungal homologues of Utp8p, and the localization of the positive charges on the conserved surface was found in all cases. Taken together, these data suggest that the positive-charge cleft of the C-terminal domain of Utp8p is involved in tRNA-binding.
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Saint-Léger, Adélaïde, Carla Bello, Pablo D. Dans, Adrian Gabriel Torres, Eva Maria Novoa, Noelia Camacho, Modesto Orozco, Fyodor A. Kondrashov i Lluís Ribas de Pouplana. "Saturation of recognition elements blocks evolution of new tRNA identities". Science Advances 2, nr 4 (kwiecień 2016): e1501860. http://dx.doi.org/10.1126/sciadv.1501860.
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Understanding the principles that led to the current complexity of the genetic code is a central question in evolution. Expansion of the genetic code required the selection of new transfer RNAs (tRNAs) with specific recognition signals that allowed them to be matured, modified, aminoacylated, and processed by the ribosome without compromising the fidelity or efficiency of protein synthesis. We show that saturation of recognition signals blocks the emergence of new tRNA identities and that the rate of nucleotide substitutions in tRNAs is higher in species with fewer tRNA genes. We propose that the growth of the genetic code stalled because a limit was reached in the number of identity elements that can be effectively used in the tRNA structure.
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Bhatta, Arjun, Christian Dienemann, Patrick Cramer i Hauke S. Hillen. "Structural basis of RNA processing by human mitochondrial RNase P". Nature Structural & Molecular Biology 28, nr 9 (wrzesień 2021): 713–23. http://dx.doi.org/10.1038/s41594-021-00637-y.
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AbstractHuman mitochondrial transcripts contain messenger and ribosomal RNAs flanked by transfer RNAs (tRNAs), which are excised by mitochondrial RNase (mtRNase) P and Z to liberate all RNA species. In contrast to nuclear or bacterial RNase P, mtRNase P is not a ribozyme but comprises three protein subunits that carry out RNA cleavage and methylation by unknown mechanisms. Here, we present the cryo-EM structure of human mtRNase P bound to precursor tRNA, which reveals a unique mechanism of substrate recognition and processing. Subunits TRMT10C and SDR5C1 form a subcomplex that binds conserved mitochondrial tRNA elements, including the anticodon loop, and positions the tRNA for methylation. The endonuclease PRORP is recruited and activated through interactions with its PPR and nuclease domains to ensure precise pre-tRNA cleavage. The structure provides the molecular basis for the first step of RNA processing in human mitochondria.
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Edwards, Ashley M., Maame A. Addo i Patricia C. Dos Santos. "Extracurricular Functions of tRNA Modifications in Microorganisms". Genes 11, nr 8 (7.08.2020): 907. http://dx.doi.org/10.3390/genes11080907.
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Transfer RNAs (tRNAs) are essential adaptors that mediate translation of the genetic code. These molecules undergo a variety of post-transcriptional modifications, which expand their chemical reactivity while influencing their structure, stability, and functionality. Chemical modifications to tRNA ensure translational competency and promote cellular viability. Hence, the placement and prevalence of tRNA modifications affects the efficiency of aminoacyl tRNA synthetase (aaRS) reactions, interactions with the ribosome, and transient pairing with messenger RNA (mRNA). The synthesis and abundance of tRNA modifications respond directly and indirectly to a range of environmental and nutritional factors involved in the maintenance of metabolic homeostasis. The dynamic landscape of the tRNA epitranscriptome suggests a role for tRNA modifications as markers of cellular status and regulators of translational capacity. This review discusses the non-canonical roles that tRNA modifications play in central metabolic processes and how their levels are modulated in response to a range of cellular demands.
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Gagnon, Matthieu G., Jinzhong Lin i Thomas A. Steitz. "Elongation factor 4 remodels the A-site tRNA on the ribosome". Proceedings of the National Academy of Sciences 113, nr 18 (18.04.2016): 4994–99. http://dx.doi.org/10.1073/pnas.1522932113.
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During translation, a plethora of protein factors bind to the ribosome and regulate protein synthesis. Many of those factors are guanosine triphosphatases (GTPases), proteins that catalyze the hydrolysis of guanosine 5′-triphosphate (GTP) to promote conformational changes. Despite numerous studies, the function of elongation factor 4 (EF-4/LepA), a highly conserved translational GTPase, has remained elusive. Here, we present the crystal structure at 2.6-Å resolution of the Thermus thermophilus 70S ribosome bound to EF-4 with a nonhydrolyzable GTP analog and A-, P-, and E-site tRNAs. The structure reveals the interactions of EF-4 with the A-site tRNA, including contacts between the C-terminal domain (CTD) of EF-4 and the acceptor helical stem of the tRNA. Remarkably, EF-4 induces a distortion of the A-site tRNA, allowing it to interact simultaneously with EF-4 and the decoding center of the ribosome. The structure provides insights into the tRNA-remodeling function of EF-4 on the ribosome and suggests that the displacement of the CCA-end of the A-site tRNA away from the peptidyl transferase center (PTC) is functionally significant.
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Underwood, D. C., H. Knickerbocker, G. Gardner, D. P. Condliffe i K. U. Sprague. "Silk gland-specific tRNA(Ala) genes are tightly clustered in the silkworm genome". Molecular and Cellular Biology 8, nr 12 (grudzień 1988): 5504–12. http://dx.doi.org/10.1128/mcb.8.12.5504-5512.1988.
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To understand the basis for tissue-specific production and accumulation of alanine tRNA in silkworms, we have examined the organization of the genes that code for silk gland-specific and constitutive alanine tRNAs. We have found that all of the silk gland-specific tRNA(Ala) genes (approximately 20) appear to be tightly clustered at a single locus in the Bombyx genome. These genes are arranged in tandem at intervals of approximately 150 base pairs. In contrast to the arrangement of the silk gland-specific tRNA(Ala) genes, most of the 20 to 30 constitutive tRNA(Ala) genes are dispersed in the genome. Silk gland-specific tRNA(Ala) genes are not amplified or grossly rearranged in the silk gland. Thus it is likely that differential transcription, rather than changes in gene number or structure, accounts for the tissue-specific accumulation of tRNA(Ala).
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Underwood, D. C., H. Knickerbocker, G. Gardner, D. P. Condliffe i K. U. Sprague. "Silk gland-specific tRNA(Ala) genes are tightly clustered in the silkworm genome." Molecular and Cellular Biology 8, nr 12 (grudzień 1988): 5504–12. http://dx.doi.org/10.1128/mcb.8.12.5504.
Pełny tekst źródłaStreszczenie:
To understand the basis for tissue-specific production and accumulation of alanine tRNA in silkworms, we have examined the organization of the genes that code for silk gland-specific and constitutive alanine tRNAs. We have found that all of the silk gland-specific tRNA(Ala) genes (approximately 20) appear to be tightly clustered at a single locus in the Bombyx genome. These genes are arranged in tandem at intervals of approximately 150 base pairs. In contrast to the arrangement of the silk gland-specific tRNA(Ala) genes, most of the 20 to 30 constitutive tRNA(Ala) genes are dispersed in the genome. Silk gland-specific tRNA(Ala) genes are not amplified or grossly rearranged in the silk gland. Thus it is likely that differential transcription, rather than changes in gene number or structure, accounts for the tissue-specific accumulation of tRNA(Ala).
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Liu, Yuchen, David J. Vinyard, Megan E. Reesbeck, Tateki Suzuki, Kasidet Manakongtreecheep, Patrick L. Holland, Gary W. Brudvig i Dieter Söll. "A [3Fe-4S] cluster is required for tRNA thiolation in archaea and eukaryotes". Proceedings of the National Academy of Sciences 113, nr 45 (24.10.2016): 12703–8. http://dx.doi.org/10.1073/pnas.1615732113.
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The sulfur-containing nucleosides in transfer RNA (tRNAs) are present in all three domains of life; they have critical functions for accurate and efficient translation, such as tRNA structure stabilization and proper codon recognition. The tRNA modification enzymes ThiI (in bacteria and archaea) and Ncs6 (in archaea and eukaryotic cytosols) catalyze the formation of 4-thiouridine (s4U) and 2-thiouridine (s2U), respectively. The ThiI homologs were proposed to transfer sulfur via cysteine persulfide enzyme adducts, whereas the reaction mechanism of Ncs6 remains unknown. Here we show that ThiI from the archaeon Methanococcus maripaludis contains a [3Fe-4S] cluster that is essential for its tRNA thiolation activity. Furthermore, the archaeal and eukaryotic Ncs6 homologs as well as phosphoseryl-tRNA (Sep-tRNA):Cys-tRNA synthase (SepCysS), which catalyzes the Sep-tRNA to Cys-tRNA conversion in methanogens, also possess a [3Fe-4S] cluster similar to the methanogenic archaeal ThiI. These results suggest that the diverse tRNA thiolation processes in archaea and eukaryotic cytosols share a common mechanism dependent on a [3Fe-4S] cluster for sulfur transfer.
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Pinto, Paola H., Alena Kroupova, Alexander Schleiffer, Karl Mechtler, Martin Jinek, Stefan Weitzer i Javier Martinez. "ANGEL2 is a member of the CCR4 family of deadenylases with 2′,3′-cyclic phosphatase activity". Science 369, nr 6503 (30.07.2020): 524–30. http://dx.doi.org/10.1126/science.aba9763.
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RNA molecules are frequently modified with a terminal 2′,3′-cyclic phosphate group as a result of endonuclease cleavage, exonuclease trimming, or de novo synthesis. During pre-transfer RNA (tRNA) and unconventional messenger RNA (mRNA) splicing, 2′,3′-cyclic phosphates are substrates of the tRNA ligase complex, and their removal is critical for recycling of tRNAs upon ribosome stalling. We identified the predicted deadenylase angel homolog 2 (ANGEL2) as a human phosphatase that converts 2′,3′-cyclic phosphates into 2′,3′-OH nucleotides. We analyzed ANGEL2’s substrate preference, structure, and reaction mechanism. Perturbing ANGEL2 expression affected the efficiency of pre-tRNA processing, X-box–binding protein 1 (XBP1) mRNA splicing during the unfolded protein response, and tRNA nucleotidyltransferase 1 (TRNT1)–mediated CCA addition onto tRNAs. Our results indicate that ANGEL2 is involved in RNA pathways that rely on the ligation or hydrolysis of 2′,3′-cyclic phosphates.
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Strobel, M. C., i J. Abelson. "Intron mutations affect splicing of Saccharomyces cerevisiae SUP53 precursor tRNA". Molecular and Cellular Biology 6, nr 7 (lipiec 1986): 2674–83. http://dx.doi.org/10.1128/mcb.6.7.2674-2683.1986.
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The Saccharomyces cerevisiae amber suppressor tRNA gene SUP53 (a tRNALeu3 allele) was used to investigate the role of intron structure and sequence on precursor tRNA splicing in vivo and in vitro. This gene encodes a pre-tRNA which contains a 32-base intervening sequence. Two types of SUP53 intron mutants were constructed: ones with an internal deletion of the natural SUP53 intron and ones with a novel intron. These mutant genes were transcribed in vitro, and the end-processed transcripts were analyzed for their ability to serve as substrates for the partially purified S. cerevisiae tRNA endonuclease and ligase. The in vitro phenotype of these mutant RNAs was correlated with the in vivo suppressor tRNA function of these SUP53 alleles after integration of the genes into the yeast genome. Analysis of these mutant pre-tRNAs, which exhibited no perturbation of the mature domain, clearly showed that intron structure and sequence can have profound effects on pre-tRNA splicing. All of the mutant RNAs, which were inefficiently spliced or unspliced, evidenced cleavage only at the 5' splice junction. Base changes in the intron proximal to the 3' splice junction could partially rescue the splicing defect. The implications of these data for tRNA endonuclease-substrate interactions are discussed.
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Strobel, M. C., i J. Abelson. "Intron mutations affect splicing of Saccharomyces cerevisiae SUP53 precursor tRNA." Molecular and Cellular Biology 6, nr 7 (lipiec 1986): 2674–83. http://dx.doi.org/10.1128/mcb.6.7.2674.
Pełny tekst źródłaStreszczenie:
The Saccharomyces cerevisiae amber suppressor tRNA gene SUP53 (a tRNALeu3 allele) was used to investigate the role of intron structure and sequence on precursor tRNA splicing in vivo and in vitro. This gene encodes a pre-tRNA which contains a 32-base intervening sequence. Two types of SUP53 intron mutants were constructed: ones with an internal deletion of the natural SUP53 intron and ones with a novel intron. These mutant genes were transcribed in vitro, and the end-processed transcripts were analyzed for their ability to serve as substrates for the partially purified S. cerevisiae tRNA endonuclease and ligase. The in vitro phenotype of these mutant RNAs was correlated with the in vivo suppressor tRNA function of these SUP53 alleles after integration of the genes into the yeast genome. Analysis of these mutant pre-tRNAs, which exhibited no perturbation of the mature domain, clearly showed that intron structure and sequence can have profound effects on pre-tRNA splicing. All of the mutant RNAs, which were inefficiently spliced or unspliced, evidenced cleavage only at the 5' splice junction. Base changes in the intron proximal to the 3' splice junction could partially rescue the splicing defect. The implications of these data for tRNA endonuclease-substrate interactions are discussed.
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Antika, Titi Rindi, Dea Jolie Chrestella, Indira Rizqita Ivanesthi, Gita Riswana Nawung Rida, Kuan-Yu Chen, Fu-Guo Liu, Yi-Chung Lee, Yu-Wei Chen, Yi-Kuan Tseng i Chien-Chia Wang. "Gain of C-Ala enables AlaRS to target the L-shaped tRNAAla". Nucleic Acids Research 50, nr 4 (31.01.2022): 2190–200. http://dx.doi.org/10.1093/nar/gkac026.
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Abstract Unlike many other aminoacyl-tRNA synthetases, alanyl-tRNA synthetase (AlaRS) retains a conserved prototype structure throughout biology. While Caenorhabditis elegans cytoplasmic AlaRS (CeAlaRSc) retains the prototype structure, its mitochondrial counterpart (CeAlaRSm) contains only a residual C-terminal domain (C-Ala). We demonstrated herein that the C-Ala domain from CeAlaRSc robustly binds both tRNA and DNA. It bound different tRNAs but preferred tRNAAla. Deletion of this domain from CeAlaRSc sharply reduced its aminoacylation activity, while fusion of this domain to CeAlaRSm selectively and distinctly enhanced its aminoacylation activity toward the elbow-containing (or L-shaped) tRNAAla. Phylogenetic analysis showed that CeAlaRSm once possessed the C-Ala domain but later lost most of it during evolution, perhaps in response to the deletion of the T-arm (part of the elbow) from its cognate tRNA. This study underscores the evolutionary gain of C-Ala for docking AlaRS to the L-shaped tRNAAla.
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Hong, Samuel, S. Sunita, Tatsuya Maehigashi, Eric D. Hoffer, Jack A. Dunkle i Christine M. Dunham. "Mechanism of tRNA-mediated +1 ribosomal frameshifting". Proceedings of the National Academy of Sciences 115, nr 44 (27.09.2018): 11226–31. http://dx.doi.org/10.1073/pnas.1809319115.
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Accurate translation of the genetic code is critical to ensure expression of proteins with correct amino acid sequences. Certain tRNAs can cause a shift out of frame (i.e., frameshifting) due to imbalances in tRNA concentrations, lack of tRNA modifications or insertions or deletions in tRNAs (called frameshift suppressors). Here, we determined the structural basis for how frameshift-suppressor tRNASufA6 (a derivative of tRNAPro) reprograms the mRNA frame to translate a 4-nt codon when bound to the bacterial ribosome. After decoding at the aminoacyl (A) site, the crystal structure of the anticodon stem-loop of tRNASufA6 bound in the peptidyl (P) site reveals ASL conformational changes that allow for recoding into the +1 mRNA frame. Furthermore, a crystal structure of full-length tRNASufA6 programmed in the P site shows extensive conformational rearrangements of the 30S head and body domains similar to what is observed in a translocation intermediate state containing elongation factor G (EF-G). The 30S movement positions tRNASufA6 toward the 30S exit (E) site disrupting key 16S rRNA–mRNA interactions that typically define the mRNA frame. In summary, this tRNA-induced 30S domain change in the absence of EF-G causes the ribosome to lose its grip on the mRNA and uncouples the canonical forward movement of the tRNAs during elongation.
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Shibata, Hirotaka S., Hiroaki Takaku, Masamichi Takagi i Masayuki Nashimoto. "The T Loop Structure Is Dispensable for Substrate Recognition by tRNase ZL". Journal of Biological Chemistry 280, nr 23 (11.04.2005): 22326–34. http://dx.doi.org/10.1074/jbc.m502048200.
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tRNA 3′-processing endoribonucleases (tRNase Z, or 3′-tRNase; EC 3.1.26.11) are enzymes that remove 3′-trailers from pre-tRNAs. An about 12-base-pair stem, a T loop-like structure, and a 3′-trailer were considered to be the minimum requirements for recognition by the long form (tRNase ZL) of tRNase Z; tRNase ZL can recognize and cleave a micro-pre-tRNA or a hooker/target RNA complex that resembles a micro-pre-tRNA. We examined four hook RNAs containing systematically weakened T stems for directing target RNA cleavage by tRNase ZL. As expected, the cleavage efficiency decreased with the decrease in T stem stability, and to our surprise, even the hook RNA that forms no T stem-loop-directed slight cleavage of the target RNA, suggesting that the T stem-loop structure is important but dispensable for substrate recognition by tRNase ZL. To analyze the effect of the T loop on substrate recognition, we compared the cleavage reaction for a micro-pre-tRNA with that for a 12-base-pair double-stranded RNA, which is the same as the micro-pre-tRNA except for the lack of the T loop structure. The observed rate constant value for the double-stranded RNA was comparable with that for the micro-pre-tRNA, whereas the Kd value for the complex with the double-stranded RNA was much higher than that for the complex with the micro-pre-tRNA. These results suggest that the T loop structure is not indispensable for the recognition, although the interaction between the T loop and the enzyme exists. Cleavage assays for such double-stranded RNA substrates of various lengths suggested that tRNase ZL can recognize and cleave double-stranded RNA substrates that are longer than 5 base pairs and shorter than 20 base pairs. We also showed that double-stranded RNA is not a substrate for the short form of tRNase Z.
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Gupta, Yash Munnalal, Kittisak Buddhachat, Surin Peyachoknagul i Somjit Homchan. "Collection of Mitochondrial tRNA Sequences and Anticodon Identification for Acheta domesticus". Materials Science Forum 967 (sierpień 2019): 65–70. http://dx.doi.org/10.4028/www.scientific.net/msf.967.65.
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The mitochondria are organelles found within eukaryotic cell, possess own small circular DNA (mtDNA) apart from the most of DNA found in cell nucleus. The transcription and translation of mtDNA requires tRNA that often encoded by mtDNA itself. The mtDNA evolves faster than genomic DNA primary due to mitochondrial dysfunction and pathogenesis. The genes of mitochondria tRNA (mt tRNA) are prone to mutate that links to mitochondrial activity and protein synthesis machinery. It is important to understand the codon use by mt tRNA for Acheta domesticus to understand evolutionary relationship within closely related species and mitochondrial protein synthesis machinery. The present study uses the High throughput RNA sequencing data to identify mt tRNA genes using to examine the codon use for mitochondrial protein synthesis process. The conservative property of tRNA secondary structure assisted identified and confirmed anchored tRNA sequences with respective amino acid anticodon according to genetic code for tRNA in mtDNA. This study provides mt tRNA sequences to understand evolution of mitochondrial tRNA of Acheta domesticus with other related species to establish phylogeny. Moreover, mt tRNAs are the exons that provides partial sequences for mitochondria DNA. The novel approach for tRNA identification will guide other studies for PCR free in silico analysis.
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Dörner, Marion, Markus Altmann, Svante Pääbo i Mario Mörl. "Evidence for Import of a Lysyl-tRNA into Marsupial Mitochondria". Molecular Biology of the Cell 12, nr 9 (wrzesień 2001): 2688–98. http://dx.doi.org/10.1091/mbc.12.9.2688.
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The mitochondrial tRNA gene for lysine was analyzed in 11 different marsupial mammals. Whereas its location is conserved when compared with other vertebrate mitochondrial genomes, its primary sequence and inferred secondary structure are highly unusual and variable. For example, eight species lack the expected anticodon. Because the corresponding transcripts are not altered by any RNA-editing mechanism, the lysyl-tRNA gene seems to represent a mitochondrial pseudogene. Purification of marsupial mitochondria and in vitro aminoacylation of isolated tRNAs with lysine, followed by analysis of aminoacylated tRNAs, show that a nuclear-encoded tRNALys is associated with marsupial mitochondria. We conclude that a functional tRNALys encoded in the nuclear genome is imported into mitochondria in marsupials. Thus, tRNA import is not restricted to plant, yeast, and protozoan mitochondria but also occurs also in mammals.
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Kazuhito, Tomizawa, i Fan-Yan Wei. "Posttranscriptional modifications in mitochondrial tRNA and its implication in mitochondrial translation and disease". Journal of Biochemistry 168, nr 5 (20.08.2020): 435–44. http://dx.doi.org/10.1093/jb/mvaa098.
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Abstract A fundamental aspect of mitochondria is that they possess DNA and protein translation machinery. Mitochondrial DNA encodes 22 tRNAs that translate mitochondrial mRNAs to 13 polypeptides of respiratory complexes. Various chemical modifications have been identified in mitochondrial tRNAs via complex enzymatic processes. A growing body of evidence has demonstrated that these modifications are essential for translation by regulating tRNA stability, structure and mRNA binding, and can be dynamically regulated by the metabolic environment. Importantly, the hypomodification of mitochondrial tRNA due to pathogenic mutations in mitochondrial tRNA genes or nuclear genes encoding modifying enzymes can result in life-threatening mitochondrial diseases in humans. Thus, the mitochondrial tRNA modification is a fundamental mechanism underlying the tight regulation of mitochondrial translation and is essential for life. In this review, we focus on recent findings on the physiological roles of 5-taurinomethyl modification (herein referred as taurine modification) in mitochondrial tRNAs. We summarize the findings in human patients and animal models with a deficiency of taurine modifications and provide pathogenic links to mitochondrial diseases. We anticipate that this review will help understand the complexity of mitochondrial biology and disease.
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Noller, Harry F., Rachel Green, Gabriele Heilek, Vernita Hoffarth, Alexander Hüttenhofer, Simpson Joseph, Inho Lee i in. "Structure and function of ribosomal RNA". Biochemistry and Cell Biology 73, nr 11-12 (1.12.1995): 997–1009. http://dx.doi.org/10.1139/o95-107.
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A refined model has been developed for the folding of 16S rRNA in the 30S subunit, based on additional constraints obtained from new experimental approaches. One set of constraints comes from hydroxyl radical footprinting of each of the individual 30S ribosomal proteins, using free Fe2+–EDTA complex. A second approach uses localized hydroxyl radical cleavage from a single Fe2+tethered to unique positions on the surface of single proteins in the 30S subunit. This has been carried out for one position on the surface of protein S4, two on S17, and three on S5. Nucleotides in 16S rRNA that are essential for P-site tRNA binding were identified by a modification interference strategy. Ribosomal subunits were partially inactivated by chemical modification at a low level. Active, partially modified subunits were separated from inactive ones by binding 3′-biotin-derivatized tRNA to the 30S subunits and captured with streptavidin beads. Essential bases are those that are unmodified in the active population but modified in the total population. The four essential bases, G926, 2mG966, G1338, and G1401 are a subset of those that are protected from modification by P-site tRNA. They are all located in the cleft of our 30S subunit model. The rRNA neighborhood of the acceptor end of tRNA was probed by hydroxyl radical probing from Fe2+tethered to the 5′ end of tRNA via an EDTA linker. Cleavage was detected in domains IV, V, and VI of 23S rRNA, but not in 5S or 16S rRNA. The sites were all found to be near bases that were protected from modification by the CCA end of tRNA in earlier experiments, except for a set of E-site cleavages in domain IV and a set of A-site cleavages in the α-sarcin loop of domain VI. In vitro genetics was used to demonstrate a base-pairing interaction between tRNA and 23S rRNA. Mutations were introduced at positions C74 and C75 of tRNA and positions 2252 and 2253 of 23S rRNA. Interaction of the CCA end of tRNA with mutant ribosomes was tested using chemical probing in conjunction with allele-specific primer extension. The interaction occurred only when there was a Watson–Crick pairing relationship between positions 74 of tRNA and 2252 of 23S rRNA. Using a novel chimeric in vitro reconstitution method, it was shown that the peptidyl transferase reaction depends on this same Watson–Crick base pair.Key words: rRNA, ribosome, tRNA, hydroxyl radical, ribosomal protein.
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Mathison, L., M. Winey, C. Soref, M. R. Culbertson i G. Knapp. "Mutations in the anticodon stem affect removal of introns from pre-tRNA in Saccharomyces cerevisiae". Molecular and Cellular Biology 9, nr 10 (październik 1989): 4220–28. http://dx.doi.org/10.1128/mcb.9.10.4220-4228.1989.
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To evaluate the role of exon domains in tRNA splicing, the anti-codon stem of proline pre-tRNAUGG from Saccharomyces cerevisiae was altered by site-directed mutagenesis of the suf8 gene. Sixteen alleles were constructed that encode mutant pre-tRNAs containing all possible base combinations in the last base pair of the anticodon stem adjacent to the anticodon loop (positions 31 and 39). The altered pre-tRNAs were screened by using an in vitro endonucleolytic cleavage assay to determine whether perturbations in secondary structure affect the intron excision reaction. The pre-tRNAs were cleaved efficiently whenever secondary structure in the anticodon stem was maintained through standard base pairing or G.U interactions. However, most of the pre-tRNAs with disrupted secondary structure were poor substrates for intron excision. We also determined the extent to which the suf8 alleles produce functional products in vivo. Each allele was integrated in one to three copies into a yeast chromosome or introduced on a high-copy-number plasmid by transformation. The formation of a functional product was assayed by the ability of each allele to suppress the +1 frameshift mutation his4-713 through four-base codon reading, as shown previously for the SUF8-1 suppressor allele. We found that alleles containing any standard base pair or G.U pair at position 31/39 in the anticodon stem failed to suppress his4-713. We could not assess in vivo splicing with these alleles because the tRNA products, even if they are made, would be expected to read a normal triplet rather than a quadruplet codon. However, all of the alleles that contained a disrupted base pair at position 31/ 39 in the anticodon stem altered the structure of the tRNA in a manner that caused frameshift suppression. Suppression indicated that splicing must have occurred to some extent in vivo even though most of the suppression alleles produced pre-tRNAs that were cleaved with low efficiency or not at all in vitro. These results have important implications for the interpretation of in vitro cleavage assays in general and for the potential use of suppressors to select mutations that affects tRNA splicing.
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Mathison, L., M. Winey, C. Soref, M. R. Culbertson i G. Knapp. "Mutations in the anticodon stem affect removal of introns from pre-tRNA in Saccharomyces cerevisiae." Molecular and Cellular Biology 9, nr 10 (październik 1989): 4220–28. http://dx.doi.org/10.1128/mcb.9.10.4220.
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To evaluate the role of exon domains in tRNA splicing, the anti-codon stem of proline pre-tRNAUGG from Saccharomyces cerevisiae was altered by site-directed mutagenesis of the suf8 gene. Sixteen alleles were constructed that encode mutant pre-tRNAs containing all possible base combinations in the last base pair of the anticodon stem adjacent to the anticodon loop (positions 31 and 39). The altered pre-tRNAs were screened by using an in vitro endonucleolytic cleavage assay to determine whether perturbations in secondary structure affect the intron excision reaction. The pre-tRNAs were cleaved efficiently whenever secondary structure in the anticodon stem was maintained through standard base pairing or G.U interactions. However, most of the pre-tRNAs with disrupted secondary structure were poor substrates for intron excision. We also determined the extent to which the suf8 alleles produce functional products in vivo. Each allele was integrated in one to three copies into a yeast chromosome or introduced on a high-copy-number plasmid by transformation. The formation of a functional product was assayed by the ability of each allele to suppress the +1 frameshift mutation his4-713 through four-base codon reading, as shown previously for the SUF8-1 suppressor allele. We found that alleles containing any standard base pair or G.U pair at position 31/39 in the anticodon stem failed to suppress his4-713. We could not assess in vivo splicing with these alleles because the tRNA products, even if they are made, would be expected to read a normal triplet rather than a quadruplet codon. However, all of the alleles that contained a disrupted base pair at position 31/ 39 in the anticodon stem altered the structure of the tRNA in a manner that caused frameshift suppression. Suppression indicated that splicing must have occurred to some extent in vivo even though most of the suppression alleles produced pre-tRNAs that were cleaved with low efficiency or not at all in vitro. These results have important implications for the interpretation of in vitro cleavage assays in general and for the potential use of suppressors to select mutations that affects tRNA splicing.
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Agmon, Ilana. "Prebiotic Assembly of Cloverleaf tRNA, Its Aminoacylation and the Origin of Coding, Inferred from Acceptor Stem Coding-Triplets". International Journal of Molecular Sciences 23, nr 24 (12.12.2022): 15756. http://dx.doi.org/10.3390/ijms232415756.
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tRNA is a key component in life’s most fundamental process, the translation of the instructions contained in mRNA into proteins. Its role had to be executed as soon as the earliest translation emerged, but the questions of the prebiotic tRNA materialization, aminoacylation, and the origin of the coding triplets it carries are still open. Here, these questions are addressed by utilizing a distinct pattern of coding triplets highly conserved in the acceptor stems from the modern bacterial tRNAs of five early-emerging amino acids. Self-assembly of several copies of a short RNA oligonucleotide that carries a related pattern of coding triplets, via a simple and statistically feasible process, is suggested to result in a proto-tRNA model highly compatible with the cloverleaf secondary structure of the modern tRNA. Furthermore, these stem coding triplets evoke the possibility that they were involved in self-aminoacylation of proto-tRNAs prior to the emergence of the earliest synthetases, a process proposed to underlie the formation of the genetic code. Being capable of autonomous materialization and of self-aminoacylation, this verifiable model of the proto-tRNA advent adds principal components to an initial set of molecules and processes that may have led, exclusively through natural means, to the emergence of life.
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MANS, Ruud M. W., Cornelis W. A. PLEIJ i Leendert BOSCH. "tRNA-like structures. Structure, function and evolutionary significance". European Journal of Biochemistry 201, nr 2 (październik 1991): 303–24. http://dx.doi.org/10.1111/j.1432-1033.1991.tb16288.x.
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