Activation of gene expression by small RNA

Small regulatory RNAs (sRNAs) commonly act to downregulate gene expression. In bacteria, however, sRNAs have also been shown to activate genes by a variety of direct or indirect mechanisms. Several sRNAs (DsrA, GImZ, RNAIII, RprA, RyhB, and Qrr) act as direct translational activators by an 'antiantisense mechanism' in the 5' mRNA region to liberate a sequestered ribosome binding site, while pairing of GadY sRNA to the 3'-end alters processing and increases stability of its target mRNA. Indirect activation includes cases of RNA mimicry in which degradation of the activating GImZ sRNA is suppressed by the highly similar GImY sRNA, or where a pseudo-target mRNA traps MicM sRNA to derepress porin synthesis.