New developments in post-transcriptional regulation of operons by small RNAs.

Small regulatory RNAs (sRNAs) are influential post-transcriptional modulators of gene expression in bacteria. They regulate gene expression by base pairing to target mRNAs, leading to inhibition of translation and/or alteration of mRNA stability. Recently, several sRNAs have been discovered to regulate genes encoded in operons. In some cases, these sRNAs regulate all the genes encoded by the polycistronic mRNA (coordinate regulation) while in other cases, only a select subset of cistrons is controlled by the sRNA (discoordinate regulation). In this point of view, mechanisms of regulation and characteristics of sRNA-mRNA interactions involving polycistronic mRNAs are described. The diversity in mechanisms represented by these few characterized examples suggests that we still have much to learn about sRNA regulation of long polycistronic messages.