Bacterial small regulatory RNAs.

Regulatory RNA molecules have crucial roles in modulating gene expression across diverse biological systems, thereby regulating multiple complex cellular programmes ranging from embryonic development to pathogenesis. In bacteria, regulatory RNAs are expressed in response to various environmental cues and stress conditions, and they are key regulators of virulence and biofilm formation, among others. Most known bacterial RNA regulators belong to the heterogeneous group of small RNAs (sRNAs), which often function together with RNA-binding proteins to base-pair with and modulate target mRNA translation and/or stability. Other bacterial sRNAs regulate protein activity, affect transcription elongation and termination, or detect foreign nucleic acids. Given that a single sRNA often regulates dozens of genes, these regulators have been recognized as rivalling transcription factors in their regulatory actions and contributions to network logic. In this Review, I summarize the regulatory functions of bacterial sRNAs, describe the molecular mechanisms that govern their expression and regulatory consequences, and discuss the many exciting open questions surrounding sRNA-mediated gene regulation in bacteria.