Molecular call and response: The physiology of bacterial small RNAs

The vital role of bacterial small RNAs (sRNAs) in cellular regulation is now well-established. Although many diverse mechanisms by which sRNAs bring about changes in gene expression have been thoroughly described, comparatively less is known about their biological roles and effects on cell physiology. Nevertheless, for some sRNAs, insight has been gained into the intricate regulatory interplay that is required to sense external environmental and internal metabolic cues and turn them into physiological outcomes. Here, we review examples of regulation by selected sRNAs, emphasizing signals and regulators required for sRNA expression, sRNA regulatory targets, and the resulting consequences for the cell. We highlight sRNAs involved in regulation of the processes of iron homeostasis (RyhB, PrrF, and FsrA) and carbon metabolism (Spot 42, CyaR, and SgrS).

► Bacterial sRNAs are important regulators with well-described molecular mechanisms.
► Relatively less is known about the effects of sRNAs on cell physiology and behavior.
► We review environmental and metabolic cues and regulators needed for sRNA activation.
► We also emphasize sRNA targets and what is known about physiological effects.
► We focus on selected sRNAs involved in iron homeostasis and carbon metabolism.