Добірка наукової літератури з теми "DNA MTase"

DNA methylation is a highly conserved epigenetic modification involved in many biological processes, including growth and development, stress response, and secondary metabolism. In the plant kingdom, cytosine-5 DNA methyltransferase (C5-MTase) and DNA demethylase (dMTase) genes have been identified in some plant species. However, to the best of our knowledge, no investigator has focused on the identification and analysis of C5-MTase and dMTase genes in tea plants (Camellia sinensis) based on genome-wide levels. In this study, eight CsC5-MTases and four dMTases were identified in tea plants. These CsC5-MTase genes were divided into four subfamilies, including CsMET, CsCMT, CsDRM and CsDNMT2. The CsdMTase genes can be classified into CsROS, CsDME and CsDML. Based on conserved domain analysis of these genes, the gene loss and duplication events occurred during the evolution of CsC5-MTase and CsdMTase. Furthermore, multiple cis-acting elements were observed in the CsC5-MTase and CsdMTase, including light responsiveness, phytohormone responsiveness, stress responsiveness, and plant growth and development-related elements. Then, we investigated the transcript abundance of CsC5-MTase and CsdMTase under abiotic stress (cold and drought) and withering processing (white tea and oolong tea). Notably, most CsC5-MTases, except for CsCMT1 and CsCMT2, were significantly downregulated under abiotic stress, while the transcript abundance of all four CsdMTase genes was significantly induced. Similarly, the same transcript abundance of CsC5-MTase and CsdMTase was found during withering processing of white tea and oolong tea, respectively. In total, our findings will provide a basis for the roles of CsC5-MTase and CsdMTase in response to abiotic stress and the potential functions of these two gene families in affecting tea flavor during tea withering processing.

Cytosine DNA methylation is highly conserved epigenetic modification involved in a wide range of biological processes in eukaryotes. It was established and maintained by cytosine-5 DNA methyltransferases (C5-MTases) in plants. Through genome-wide identification, eight putative SmC5-MTase genes were identified from the genome of Salvia miltiorrhiza, a well-known traditional Chinese medicine material and an emerging model medicinal plant. Based on conserved domains and phylogenetic analysis, eight SmC5-MTase genes were divided into four subfamilies, including MET, CMT, DRM and DNMT2. Genome-wide comparative analysis of the C5-MTase gene family in S. miltiorrhiza and Arabidopsis thaliana, including gene structure, sequence features, sequence alignment and conserved motifs, was carried out. The results showed conservation and divergence of the members of each subfamily in plants. The length of SmC5-MTase open reading frames ranges widely from 1,152 (SmDNMT2) to 5,034 bp (SmMET1). The intron number of SmC5-MTases varies between 7 (SmDRM1) and 20 (SmCMT1 and SmCMT2b). These features were similar to their counterparts from Arabidopsis. Sequence alignment and conserved motif analysis showed the existence of highly conserved and subfamily-specific motifs in the C5-MTases analyzed. Differential transcript abundance was detected for SmC5-MTases, implying genome-wide variance of DNA methylation in different organs and tissues. Transcriptome-wide analysis showed that the transcript levels of all SmC5-MTase genes was slightly changed under yeast extract and methyl jasmonate treatments. Six SmC5-MTases, including SmMET1, SmCMT1, SmCMT2a, SmCMT2b, SmCMT3 and SmDRM1, were salicylic acid-responsive, suggesting the involvement of SmC5-MTases in salicylic acid-dependent immunity. These results provide useful information for demonstrating the role of DNA methylation in bioactive compound biosynthesis and Dao-di herb formation in medicinal plants.

In bacteria, DNA-methyltransferase are responsible for DNA methylation of specific motifs in the genome. This methylation usually occurs at a very high rate. In the present study, we studied the MTases encoding genes found in the entomopathogenic bacteria Xenorhabdus. Only one persistent MTase was identified in the various species of this genus. This MTase, also broadly conserved in numerous Gram-negative bacteria, is called Dam: DNA-adenine MTase. Methylome analysis confirmed that the GATC motifs recognized by Dam were methylated at a rate of >99% in the studied strains. The observed enrichment of unmethylated motifs in putative promoter regions of the X. nematophila F1 strain suggests the possibility of epigenetic regulations. The overexpression of the Dam MTase responsible for additional motifs to be methylated was associated with impairment of two major phenotypes: motility, caused by a downregulation of flagellar genes, and hemolysis. However, our results suggest that dam overexpression did not modify the virulence properties of X. nematophila. This study increases the knowledge on the diverse roles played by MTases in bacteria.

DNA methyltransferases (MTases) can be regarded as biomarkers, as demonstrated by many studies on genetic diseases. Many researchers have developed biosensors to detect the activity of DNA MTases, and nucleic acid amplification, which need other probe assistance, is often used to improve the sensitivity of DNA MTases. However, there is no integrated probe that incorporates substrates and template and primer for detecting DNA MTases activity. Herein, we first designed a padlock probe (PP) to detect DNA MTases, which combines target detection with rolling circle amplification (RCA) without purification or other probe assistance. As the substrate of MTase, the PP was methylated and defended against HpaII, lambda exonuclease, and ExoI cleavage, as well as digestion, by adding MTase and the undestroyed PP started RCA. Thus, the fluorescent signal was capable of being rapidly detected after adding SYBRTM Gold to the RCA products. This method has a detection limit of approximately 0.0404 U/mL, and the linear range was 0.5–110 U/mL for M.SssI. Moreover, complex biological environment assays present prospects for possible application in intricacy environments. In addition, the designed detection system can also screen drugs or inhibitors for MTases.

Cytosine-5 DNA methyltransferases (C5-MTases) and methyl-CpG-binding-domain (MBD) genes can be co-expressed. They directly control target gene expression by enhancing their DNA methylation levels in humans; however, the presence of this kind of cooperative relationship in plants has not been determined. A popular garden plant worldwide, petunia (Petunia hybrida) is also a model plant in molecular biology. In this study, 9 PhC5-MTase and 11 PhMBD proteins were identified in petunia, and they were categorized into four and six subgroups, respectively, on the basis of phylogenetic analyses. An expression correlation analysis was performed to explore the co-expression relationships between PhC5-MTases and PhMBDs using RNA-seq data, and 11 PhC5-MTase/PhMBD pairs preferentially expressed in anthers were identified as having the most significant correlations (Pearson’s correlation coefficients > 0.9). Remarkably, the stability levels of the PhC5-MTase and PhMBD pairs significantly decreased in different tissues and organs compared with that in anthers, and most of the selected PhC5-MTases and PhMBDs responded to the abiotic and hormonal stresses. However, highly correlated expression relationships between most pairs were not observed under different stress conditions, indicating that anther developmental processes are preferentially influenced by the co-expression of PhC5-MTases and PhMBDs. Interestingly, the nuclear localization genes PhDRM2 and PhMBD2 still had higher correlations under GA treatment conditions, implying that they play important roles in the GA-mediated development of petunia. Collectively, our study suggests a regulatory role for DNA methylation by C5-MTase and MBD genes in petunia anther maturation processes and multi-stress responses, and it provides a framework for the functional characterization of C5-MTases and MBDs in the future.

DNA MTases (methyltransferases) catalyse the transfer of methyl groups to DNA from AdoMet (S-adenosyl-L-methionine) producing AdoHcy (S-adenosyl-L-homocysteine) and methylated DNA. The C5 and N4 positions of cytosine and N6 position of adenine are the target sites for methylation. All three methylation patterns are found in prokaryotes, whereas cytosine at the C5 position is the only methylation reaction that is known to occur in eukaryotes. In general, MTases are two-domain proteins comprising one large and one small domain with the DNA-binding cleft located at the domain interface. The striking feature of all the structurally characterized DNA MTases is that they share a common core structure referred to as an ‘AdoMet-dependent MTase fold’. DNA methylation has been reported to be essential for bacterial virulence, and it has been suggested that DNA adenine MTases (Dams) could be potential targets for both vaccines and antimicrobials. Drugs that block Dam could slow down bacterial growth and therefore drug-design initiatives could result in a whole new generation of antibiotics. The transfer of larger chemical entities in a MTase-catalysed reaction has been reported and this represents an interesting challenge for bio-organic chemists. In general, amino MTases could therefore be used as delivery systems for fluorescent or other reporter groups on to DNA. This is one of the potential applications of DNA MTases towards developing non-radioactive DNA probes and these could have interesting applications in molecular biology. Being nucleotide-sequence-specific, DNA MTases provide excellent model systems for studies on protein–DNA interactions. The focus of this review is on the chemistry, enzymology and structural aspects of exocyclic amino MTases.

Abstract DNA chemical modifications, including methylation, are widespread and play important roles in prokaryotes and viruses. However, current knowledge of these modification systems is severely biased towards a limited number of culturable prokaryotes, despite the fact that a vast majority of microorganisms have not yet been cultured. Here, using single-molecule real-time sequencing, we conducted culture-independent ‘metaepigenomic’ analyses (an integrated analysis of metagenomics and epigenomics) of marine microbial communities. A total of 233 and 163 metagenomic-assembled genomes (MAGs) were constructed from diverse prokaryotes and viruses, respectively, and 220 modified motifs and 276 DNA methyltransferases (MTases) were identified. Most of the MTase genes were not genetically linked with the endonuclease genes predicted to be involved in defense mechanisms against extracellular DNA. The MTase-motif correspondence found in the MAGs revealed 10 novel pairs, 5 of which showed novel specificities and experimentally confirmed the catalytic specificities of the MTases. We revealed novel alternative specificities in MTases that are highly conserved in Alphaproteobacteria, which may enhance our understanding of the co-evolutionary history of the methylation systems and the genomes. Our findings highlight diverse unexplored DNA modifications that potentially affect the ecology and evolution of prokaryotes and viruses in nature.

DNA methylation plays an indispensable role in genome stability, regulation of gene expression and plant stress response. It is mediated by DNA methyltransferases (MTases). Twelve putative MTases of P. betulaefolia were identified and were classified into MET1, CMT, DRM2 and Dnmt2 groups based on the organization of various characteristic domains. Three pairs of paralogous genes were identified with the Ka/Ks ratio varied from 0.232 for PbeMET1a and PbeMET1b to 0.251 for PbeCMT2 and PbeCMT3, respectively. In addition, the Ka/Ks ratio for nine pairs of orthologous gene pairs between P. betulaefolia and apple were varied from 0.053 for PbeDRM3 and MD17G1031900 to 0.278 for PbeDnmt2b and MD15G1120500, respectively. All the 12 members of MTase genes were located on nine chromosomes out of 17 P. betulaefolia chromosomes with highly conserved protein sequence structures. The isoelectric points (pI) of MTases ranged from 4.74 to 7.24, while molecular weight varied from 35.99 to 174.32. The expression profiles of MTase and other salt-responsive genes under salt stress treatment revealed their important roles involved in salt response in P. betulaefolia. Furthermore, three selected salt-responsive genes (PbeNHX2.1, PbeCBL2 and PbeAKT2) were found altered in methylation level of promoters (which contain CpG islands) under salt stress. Especially, the PbeAKT2 promoter regions showed high CHG and CHH methylation types. Our study provided a genome-wide survey of the MTase gene family and highlighted their roles in salt response. These results also provided an effective way for the breeding and improvement of salt-tolerant pear varieties.

Abstract Gene expression is regulated at many levels including co- or post-transcriptionally, where chemical modifications are added to RNA on riboses and bases. Expression control via RNA modifications has been termed ‘epitranscriptomics’ to keep with the related ‘epigenomics’ for DNA modification. One such RNA modification is the N6-methylation found on adenosine (m6A) and 2′-O-methyladenosine (m6Am) in most types of RNA. The N6-methylation can affect the fold, stability, degradation and cellular interaction(s) of the modified RNA, implicating it in processes such as splicing, translation, export and decay. The multiple roles played by this modification explains why m6A misregulation is connected to multiple human cancers. The m6A/m6Am writer enzymes are RNA methyltransferases (MTases). Structures are available for functionally characterized m6A RNA MTases from human (m6A mRNA, m6A snRNA, m6A rRNA and m6Am mRNA MTases), zebrafish (m6Am mRNA MTase) and bacteria (m6A rRNA MTase). For each of these MTases, we describe their overall domain organization, the active site architecture and the substrate binding. We identify areas that remain to be investigated, propose yet unexplored routes for structural characterization of MTase:substrate complexes, and highlight common structural elements that should be described for future m6A/m6Am RNA MTase structures.

Abnormal DNA methylation patterns caused by altered DNA methyltransferase (MTase) activity are closely associated with cancer. Herein, using DNA adenine methylation methyltransferase (Dam MTase) as a model analyte, we designed an allosteric molecular beacon (aMB) for sensitive detection of Dam MTase activity.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biological Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 164-183).
Cancer causes 13% of all deaths worldwide. Inflammation-mediated cancer accounts for ~15% of all malignancies, strongly necessitating investigation of the molecular interactions at play. Inflammatory reactive oxygen and nitrogen species (RONs), including peroxynitrite and nitric oxide (NO'), may potentiate malignancy. We hypothesize that the base excision repair (BER) pathway modulates susceptibility to malignancy, by modulating the BER-intermediate levels, large scale genomic rearrangements and toxicity following exposure to RONs. We further hypothesize that DNA methyltransferases are responsible for the memory of genotoxic insult, and the epigenetic propagation of genomic instability, following exposure to genotoxins. Here, we exploited cell lines engineered to carry deficiencies in BER to study repair of DNA damage induced by RONs. Toxicity and BER-intermediate levels were evaluated in XRCC1 proficient and deficient cells, following exposure to the peroxynitrite donor, SIN-1 and to NO*. Using the alkaline comet assay, we find that while XRCC1 proficient and deficient CHO cells incur equivalent levels of SIN-1 induced BER-intermediates, the XRCC1 null cells are more sensitive to killing by SIN-1, as assessed by clonogenic survival. Furthermore, using bioreactors to expose CHO cells to NO', we found that the BER-intermediate levels measured in XRCC1 null cells were lower than in WI cells. We found that while XRCC1 can facilitate AAG-mediated excision of the inflammation-associated base lesions ethenoadenine and hypoxanthine, in vitro; XRCC1 deficient human cells were no more susceptible to NO' than WT cells. However, in live glioblastoma cells, XRCC1 is acting predominantly downstream of AAG glycosylase. This work is some of the first to assess the functional role of XRCC1, in response to RONs and suggests complexities in the role of XRCC1. We also demonstrate that the underlying basis for the memory of a genotoxic insult and the subsequent propagation of genomic instability is dependent on the DNA methyltransferases, Dnmtl and Dnmt3a. We found that a single exposure led to long-term genome destabilizing effects that spread from cell to cell, and therefore provided a molecular mechanism for these persistent bystander effects. Collectively, our findings impact current understanding of cancer risk and suggest mechanisms for suppressing genomic instability, following exposure to inflammatory genotoxins.
by James T. Mutamba.
Ph.D.

Enzyme DNA methylation is an important biochemical process that imprints DNA with additional information. DNA methylation is catalyzed by S-adenosyl-L-methionine (AdoMet)-dependent methyltraferases (MTases). Prokaryotic DNA MTases are usually components of restriction-modification(R-M) systems that enable cells to resist propagation of foreign genomes that would otherwise kill them. Based on the position methyl group transfer on the bases in DNA, MTases are classified into two groups-exocyclic or amino MTases and endocyclic or ring MTases. The amino MTases methylate exocyclic amino nitrogen to form either N6-methyladenine or n4-methycytosine. N6-methyaladenine is mostly found in the genomes of bacteria, archaea protists and fungi. Helicobacter pylori is a gram-negative, flagellated, fastidious bacterium that colonizes the highly acidic environment of the gastric mucosa. Frequently and persistence of H.paylori infection in humans make it attractive model for studying the host- pathogen interaction mechanisms. Analysis of the genome sequence of H.pylori strains 26695, J99.HPAGI, and G27 revealed an abundance of restriction-modification (R-M) systems. Most of the R-M system genes are either conserved among the strains or specific to each strain. Strain specific genes are responsible for different phenotypes in several host adapted pathogens such as H.pylori. Many of the R-M gene homologues exhibit different usages of condon bias and lower G+C content from the average genes suggesting horizontal transfer of the R-M system genes in H. Pylori. Genome analysis of strain 26695 showed the presence of three putative type III R-M systems and hp0592-hp0593 constitutes one such type III R-M system. Based on the conserved motif arrangements, HP0593 MTases belongs to the subgroups of MTases. The amino acid sequence of HP0593 MTases has 38% sequence identity to Ecop11 MTases and EcoP151 MTase, both of which belongs to type IIIR-M systems therefore, it was important to study in detail previously unexplored role of this putative type III DNA MTase (HP0593) in H. Pylori. Investigation of methyltransferease activity and sequence specifically of putative DNA adenine MTase (HP0593) HP0593 (N6-adenine) - DNA MTase is a member of a type III R-M system in H. pylori strain 26695. HP0593 MTase has been cloned, over expressed and purified heterologously in Escherichia coli. Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) was carried out with purified HP0593 and profile showed a single peak with expected molecular mass of 70.6kDa. The protein was determined as-5.8. HP0593 MTase exits predominantly as monomer and a small fraction as dimer in solution as determined by size exclusion chromatography and glutaraldehyde cross-linking studies. The recognition sequence of the purified MTase was determined as 5’GCAG-3’ and the target base of methylation is adenine. Dot-blot assay using antibodies that reacted specifically with DNA containing m6A modification confirmed that HP0593 MTase is an adenine specific MTase. Exocyclic MTase have a conserved catalytic motif (D/N/S/SPPY/F/W). Most interestingly, the amino acid sequence analysis of HP0593 MTase revealed the presence of a PCQ-like motif, which is the catalytic motif for C5-cytosine MTase in addition to DPPY motif. In order to check the role of both these MTase by glycine. HP0593 –Y107G and C54G mutant proteins were purified to near homogeneity. It was found that the Y107G mutant protein was catalytically inactive as compared to wild-type HP0593 MTase. On the other hand the C54G mutant protein was found to be as active as the wild-type HP0593 MTase indicating that HP0593 MTase is an adenine MTase and not a C5- cytosine MTase. Kinetic and catalytic properties of HP0593 DNA adenine methyltransferase DNA binding studies were carried out by electrophoretic mobility shift assay using DNA having cognate site and either in absence or presence of AdoHcy or sinefungin. In all the three cases two different DNA-protein complexes were observed-a fast running complex I and a slow running complex 2. It can be surmised that the fast running complex could be HP0593 monomer-DNA and the slow running complex could be a HP0593 dimer-DNA complex. With non specific DNA (lacking 5’-GCAG-3’ sequences) no complexes were formed even in the presence of cofactors. Based on the above observations it is suggested that a specific interactions of HP0593 MTase with DNA occurs on cognate recognition site. The activity of HP0593 MTase is optional at pH 5.5. This is a unique property in context of natural adaptation of H. pylori in its acidic niche. When initial velocities were plotted against varying concentrations of duplex DNA having a single 5’GCAG-3’ site a rectangular hyperbola was obtained confirming that HP0593 MTase obeys michaelis menten kinetics. From non-linear regression analysis of the plot of initial velocity versus DNA concentration Km (DNA) and kcat were calculated. Analysis of initial velocity with AdoMet as a substrate showed that two molecules of AdoMet bind to HP0593 MTase. The nonlinear dependence of methylation activity on enzyme concentration indicated that more than one molecule of methylation activity on enzyme concentration indicated that more than one molecule of enzyme is required for its activity. Metal ion cofactors such as CO 2, Mn2+ and Mg2+ stimulated the HP09593 MTase activity. As Mn2+ showed maximum stimulation of methyaltion activity compared to other metal ions, surface plasmon resonance spectroscopy was used to determine the kinetics of DNA binding by HP0593 MTase in the absence and presence of Mn2+. In the presence of Mn2+, HP0593 MTase showed~1000-fold increase in affinity to duplex DNA. DNA MTase bind substrates in random or sequential order. Preincubation study demonstrated that the preformed enzyme-DNA complex is competent than the preformed enzyme-AdoMet complex. This suggests that MTase binds to DNA first followed by AdoMet. Isotope partitioning analysis indicated that HP0593 MTase shows a distributive mechanism of methylation DNA having more than one recognition site. Effects of inactivation of HP0593 DNA MTase in Helicobacter pylori 26695 strain and its functional role. DNA dot-blot assay using hp0593 gene specific primer showed that this gene is present in 25.15% of the clinical strains checked suggesting that hp0593 is strain-specific gene. Strain-specific genes in many host-adapted pathogene impart strain specific phenotype. Wild-type 26695 strain grew slightly faster at the initial phase of growth in PH 4.5 compared to pH 7.4. A~5-fold enhanced level of hp0593 mRNA expression was growth under acidic condition HP0593 MTase could play an important role in H. pylori physiology through methylation. To elucidate the possible role(s) played by the MTase in H.pylori physiology, an hp0593 knock-out in 26695 strain was generated by chloramphenecol cassette mediated insertional gene inactivation. Growth kinetic study was carried out with both wild-type and hp0593 knock-out strain at pH7.4, the growth of the hp0593 strain. At pH 4.5 no major differences were observed in the growth compared to the wild-type hp0593 knock-out strain. To further investigate the effect of the knock-out, cell-morphology study was carried out after growing the strains at pH 7.4 till mid-exponential phase. Transmission electron microscopy studies reveled changes in cell shape, presence of sheathed structure and production of outer membrane vesicles (OMVs) in the hp0593 knock out strain. OMVs contain effectors molecules during infection helps in pathogenicity caused by H.pylori.This is the first report where inactivation of DNA MTase causes shedding of vesicles. OMVs are also known to modulate the production of IL-8 by gastic epitheial cells. To check weather H.pylori strains could produce IL-8, both wild-type and hp0593 knock-out strains were co-cultured with AGS cell infected with the hp0593 knock out strain. This was further confirmed by semi-quantitative RT-PCR analysis. To analyze the different phenotypes observed in the hp0593 knock-out strain, transcriptome profile were compared by microarray and RT-PCR analysis. In thehp0593 knock-out strain peptidologlycan and murein synthesis genes like pbp2, murC and neu4 showed upregulation which could be responsible for the changes in cell shape presence of sheathed structure and OMVs production. The RT-PCR data showed ~9-fold down-regulation of dank chaperone which might play a key role in slow growth phenotype in the hp0593 knock-out strain. Considering the occurrence of GCAG sequence in the potential promoter regions of physiologically important genes such as dank, neuA, murC, fliH, filP and cag5, the results presented in this study provide impetus for exploring the role of HP0593 DNA MTase in the cellular processes of H.pylori. However, R-M systems are not absolutely essential, but different methylation patterns may contribute to strain-specific epigenetic gene regulation and may contribute to variability among the strains.

This article presents the results of the construction of an Archaeological Predictive Spatial Model based on the analysis of a set of variables. The main objective of this study is to identify areas of archaeological potential for archaeological exploration, for the Médio Tejo Region. This areas are more likely to occur in new sites, through the application of predictive spatial models, starting from a base of geographic data from archaeological sites compiled and updated in their various chronologies, and modeled through Geographic Information Systems, within the framework of the MTAS research project, supported by FCT. Thus, through an essentially statistical, descriptive and univariate methodology and using two methods - the method of binary addition and the method of weights - the areas with potential for prospecting new archaeological sites were obtained for the Médio Tejo Region.