sRNA-mediated control in bacteria: An increasing diversity of regulatory mechanisms

Small regulatory RNAs (sRNAs) act as post-transcriptional regulators controlling bacterial adaptation to environmental changes. Our current understanding of the mechanisms underlying sRNA-mediated control is mainly based on studies in Escherichia coli and Salmonella. Ever since the discovery of sRNAs decades ago, these Gram-negative species have served as excellent model organisms in the field of sRNA biology. More recently, the role of sRNAs in gene regulation has become the center of attention in a broader range of species, including Gram-positive model organisms. Here, we highlight some of the most apparent similarities and differences between Gram-negative and Gram-positive bacteria with respect to the mechanisms underlying sRNA-mediated control. Although key aspects of sRNA regulation appear to be highly conserved, novel themes are arising from studies in Gram-positive species, such as a clear abundance of sRNAs acting through multiple C-rich motifs, and an apparent lack of RNA-binding proteins with chaperone activity. •Bacterial sRNAs are post-transcriptional regulators of important cellular processes.•Key aspects of sRNA regulation appear to be conserved across bacterial species.•RNA chaperones often mediate sRNA-mRNA interactions in Gram-negative species.•The RNA chaperone Hfq is either absent or dispensable in Gram-positive species.•Many Gram-positive sRNAs rely on C- or CU-rich motifs for base pairing.