Small Regulatory RNAs in Bacteria

Abstract

Intergenic regions of bacteria contain small regulatory ribonucleic acid (sRNA) genes whose transcripts control expression of distal genes. These transcripts, referred to as sRNAs, primarily act at the level of translation where they bind messenger ribonucleic acids (mRNAs) and inhibit or activate a target mRNA. Base pairing with mRNAs is generally imperfect and can include noncanonical base pairs. The RNA chaperone protein Hfq is involved in many RNA/RNA interactions and ribonucleases RNase E and RNase III have been implicated in destabilisation of target mRNAs. Many sRNAs can inhibit multiple mRNAs; however, some sRNAs bind proteins and can regulate transcription or translation indirectly. Some act like ‘sponges’ that bind and sequester proteins involved in global gene regulation. Many sRNA genes are activated by environmental stress factors, and the sRNA genes have complex upstream regulatory sites. Further insight into broad functions of sRNAs comes from human host cells infected by pathogenic bacteria, which reveals a role of sRNA in both virulence and response in human host cell molecular functions, for example changes in long noncoding RNAs and microRNAs. Bacterial regulatory RNAs are proving to be remarkable factors in both cell physiology and bacterial pathogenesis and these RNAs have opened a new world in molecular biology. Key Concepts Small regulatory RNA genes have been found in most bacterial species. sRNA transcripts are generally less than 200 nt. sRNAs can control gene expression at the level of translation or transcription. sRNAs respond to environmental or internal stress conditions. sRNAs generally form small and imperfect RNA/RNA base pairing with target mRNA; noncanonical base pairs can also be present. sRNAs can inhibit translational and/or induce degradation of target mRNA. Many sRNAs regulate multiple target mRNAs. sRNAs can indirectly regulate the expression of global genes, some by binding proteins that control gene expression. sRNAs can play a major role in bacterial pathogenicity and influence eukaryotic host molecular functions such as levels of host cell microRNA and long noncoding RNA.