Gotowa bibliografia na temat „Ribonucleic antiterminato”

BglG/LicT-like proteins are transcriptional antiterminators that prevent termination of transcription at intrinsic terminators by binding to ribonucleic antiterminator (RAT) sites and stabilizing an RNA conformation which is mutually exclusive with the terminator structure. The known RAT sites, which are located in intergenic regions of sugar utilization operons, show low sequence conservation but significant structural analogy. To assess the prevalence of RATs in bacterial genomes, we employed bioinformatic tools that describe RNA motifs based on both sequence and structural constraints. Using descriptors with different stringency, we searched the genomes of <i>Escherichia</i><i>coli</i> K12, uropathogenic <i>E. coli</i> and <i>Bacillus subtilis</i> for putative RATs. Our search identified all known RATs and additional putative RAT elements. Surprisingly, most putative RATs do not overlap an intrinsic terminator and many reside within open reading frames (ORFs). The ability of one of the putative RATs, which is located within an antiterminator-encoding ORF and does not overlap a terminator, to bind to its cognate antiterminator protein in vitro and in vivo was confirmed experimentally. Our results suggest that the capacity of RAT elements has been exploited during evolution to mediate activities other than antitermination, for example control of transcription elongation or of RNA stability.

An open reading frame (ORF) that would encode a putative antiterminator protein (LicT) of the BglG family was identified in the genomic DNA sequence of Streptococcus mutans. A DNA sequence that would encode a potential ribonucleic antiterminator (RAT) site in the mRNA at which the putative antitermination protein LicT would bind was located immediately downstream from this ORF. These putative antitermination components are upstream of a glucose-independent β-glucoside-utilization system that is responsible for aesculin utilization by S. mutans NG8 in the presence of glucose. It was hypothesized that these putative regulatory components were an important mechanism that was involved with the controlled expression of the S. mutans bglP locus. A strain of S. mutans containing a licT : : Ω-Kan2 insertional mutation was created. This strain could not hydrolyse aesculin in the presence of glucose. The transcriptional activity associated with other genes from the bgl regulon was determined in the licT : : Ω-Kan2 genetic background using lacZ transcriptional fusions and β-galactosidase assays to determine the effect of LicT on these loci. The LicT protein had no significant effect on the expression of the bglC promoter, a regulator of the bglA locus. However, it is essential for the optimal expression of bglP. These data correlate with the phenotype observed on aesculin plates for the S. mutans wild-type strain NG8 and the licT : : Ω-Kan2 strain. Thus, the glucose-independent β-glucoside-specific phosphotransferase system (PTS) regulon in S. mutans relies on LicT for BglP expression and, in turn, aesculin transport in the presence of glucose. Interestingly, LicT also seems to negatively regulate the expression of the bglA promoter region. In addition, the presence of the S. mutans licT gene has been shown to be able to activate a cryptic β-glucoside-specific operon found in Escherichia coli.

ABSTRACT In Lactobacillus casei ATCC 393, the chromosomally encoded lactose operon, lacTEGF, encodes an antiterminator protein (LacT), lactose-specific phosphoenolpyruvate-dependent phosphotransferase system (PTS) elements (LacE and LacF), and a phospho-β-galactosidase. lacT, lacE, andlacF mutant strains were constructed by double crossover. The lacT strain displayed constitutive termination at a ribonucleic antiterminator (RAT) site, whereas lacE andlacF mutants showed an inducer-independent antiterminator activity, as shown analysis of enzyme activity obtained from transcriptional fusions of lac promoter (lacp) and lacpΔRAT with the Escherichia coli gusAgene in the different lac mutants. These results strongly suggest that in vivo under noninducing conditions, the lactose-specific PTS elements negatively modulate LacT activity. Northern blot analysis detected a 100-nucleotide transcript starting at the transcription start site and ending a consensus RAT sequence and terminator region. In a ccpA mutant, transcription initiation was derepressed but no elongation through the terminator was observed in the presence of glucose and the inducing sugar, lactose. Full expression oflacTEGF was found only in a man ccpA double mutant, indicating that PTS elements are involved in the CcpA-independent catabolite repression mechanism probably via LacT.

Enterococcus faecalis is a commensal bacterium of the gastrointestinal tract but also a major nosocomial pathogen. This bacterium uses regulators like BglG/SacY family of transcriptional antiterminators to adapt its metabolism during host colonization. In this report, we investigated the role of the BglG/SacY family antiterminator NagY in the regulation of the nagY-nagE operon in presence of N-acetylglucosamine, with nagE encoding a transporter of this carbohydrate, as well as the expression of the virulence factor HylA. We showed that this last protein is involved in biofilm formation and glycosaminoglycans degradation that are important features in bacterial infection, confirmed in the Galleria mellonella model. In order to elucidate the evolution of these actors, we performed phylogenomic analyses on E. faecalis and Enterococcaceae genomes, identified orthologous sequences of NagY, NagE, and HylA, and we report their taxonomic distribution. The study of the conservation of the upstream region of nagY and hylA genes showed that the molecular mechanism of NagY regulation involves ribonucleic antiterminator sequence overlapping a rho-independent terminator, suggesting a regulation conforming to the canonical model of BglG/SacY family antiterminators. In the perspective of opportunism understanding, we offer new insights into the mechanism of host sensing thanks to the NagY antiterminator and its targets expression.