6S / SsrS RNA

The structure of 6S RNA was defined in 1971. The secondary structure consists of two irregular helical stem regions, making a large core loop which is called a central knot. == Function and Regulation ==

The function of 6S RNA is to regulate transcription for E. coli cell survival because it is essential in the process. 6S RNA specifically associates with RNA polymerase holoenzyme containing the sigma70 specificity factor. This interaction represses expression from sigma70-dependent promoters during stationary phase. Which will lead to activate the transcription from sigma 70 dependent promoters. Therefore, during the change in E. coli from logarithmic growth to stationary phase, the 6S RNA performs as a regulator of transcription. 6S RNA homologs have recently been identified in most bacterial genomes. Polymerase holoenzyme, which contains the housekeeping sigma factor and it can be expressed during different stages of growth. In many Pseudomonadota, 6S RNA may be processed from a transcript encoding homologs of the E. coli YgfA protein, which is a putative methenyltetrahydrofolate synthetase. Diverged 6S RNAs have been identified in additional bacterial lineages. The purD RNA motif has been experimentally shown to overlap with 6S RNA. == Summary ==

The recently discovered homologs of 6S are two Bacillus subtilis RNAs and cyanobacterial RNAs. Two 6S RNA, 6S-1 and 2 along with their encoding genes bsrA and B present at various positions of a genome. In stationary phase, deletion of 6S-1 in B. subtilis results in inhibition of its growth. The absence of 6S-2 RNA, on the other hand, does not appear to influence growth and sporulation in the stationary phase. 6S RNA conserved feature shows that it binds to the RNA polymerase by replicating the structure of DNA template. Promoter-dependent transcriptional regulation is mediated by 6S RNA as some of the promoters may be down-regulated and some are insensitive in the presence of 6S RNA. Gene expression studies revealed that 6S RNA is integrated in different global pathways e.g., it regulates various factors that influence transcription like Crp, FNR etc. and translation mechanism. Scientist discovered that 6S RNA binds with the active site of RNA polymerase and can serve as a template for RNA synthesis required for the RNA synthesis. It down-regulates transcription from 3´-5´fold at various promoters but doesn't inhibit transcription during late stationary phase. In a nutrient-deficient environment, 6S RNA control transcription leads to altered cell survival, possibly through redirecting resource consumption. 6S RNA is a regulator of RNA polymerase and abundantly present in bacteria. Studies has shown that the 6S RNA forms a complex with RNA polymerase to initiate transcription. Lack of 6S RNA in cells result in altered phenotypes. Structural and functional analyses showed the interactions between RNA polymerase and E. coli 6S RNA. The functional variety of 6S RNAs was discovered by genome-wide transcriptome studies. Numerous recent investigations have suggested that 6S RNA serves as a guardian, regulating the efficient utilisation of cellular resources under restricted conditions and stress. By interacting with the sigma 70-dependent RNA polymerase holoenzyme in the stationary phase, high abundant 6S RNA is discovered to influence gene transcription, resulting in bacterial response regulation to challenges such as hunger. == References ==