Mechanism of RNA silencing by Hfq-binding small RNAs.

The stress-induced small RNAs SgrS and RyhB in Escherichia coli form a specific ribonucleoprotein complex with RNAse E and Hfq resulting in translation inhibition, RNAse E-dependent degradation of target mRNAs. Translation inhibition is the primary event for gene silencing and degradation of these small RNAs is coupled with the degradation of target mRNAs. The crucial base-pairs for action of SgrS are confined to the 6 nt region overlapping the Shine-Dalgarno sequence of the target mRNA. Hfq accelerates the rate of duplex formation between SgrS and the target mRNA. Membrane localization of target mRNA contributes to efficient SgrS action by competing with ribosome loading.