DsrA

DsrA is a small regulatory RNA (sRNA) found in Escherichia coli and related bacteria. As a noncoding RNA, it functions in post-transcriptional gene regulation by base-pairing with target mRNAs to influence their translation and stability. DsrA is typically about 80–100 nucleotides in length and operates with the RNA chaperone Hfq to facilitate regulatory interactions.

The best-characterized action of DsrA is the positive regulation of the stationary-phase sigma factor RpoS. By binding to the 5' untranslated region of rpoS mRNA, DsrA alters the mRNA structure to expose the ribosome binding site, thereby increasing RpoS translation and promoting the general stress response. DsrA also contributes to broader regulatory effects by repressing the translation of hns mRNA, which encodes a global transcriptional silencer. Reduced H-NS levels can lead to derepression of a wide set of genes, including those involved in stress responses.

In addition to these primary targets, transcriptome studies have identified other potential mRNA targets, suggesting that DsrA participates in a broader regulatory network that governs responses to environmental stress, metabolism, and possibly virulence in some species. Expression of DsrA is regulated by growth phase and environmental conditions and is thought to be more prominent under stress conditions that require adaptive gene expression. The activity of DsrA, like other sRNAs, depends on cellular cofactors such as Hfq and can be influenced by RNA processing enzymes.

Overall, DsrA is a key component of bacterial post-transcriptional regulation, contributing to the fine-tuning of stress responses and altering global gene expression through targeted interactions with multiple mRNAs.