Mechanisms for Hfq-Independent Activation of by DsrA, a Small RNA, in .

Many small RNAs (sRNAs) regulate gene expression by base pairing to their target messenger RNAs (mRNAs) with the help of Hfq in . The sRNA DsrA activates translation of the mRNA in an Hfq-dependent manner, but this activation ability was found to partially bypass Hfq when DsrA is overproduced. The precise mechanism by which DsrA bypasses Hfq is unknown. In this study, we constructed strains lacking all three -activating sRNAs (i.e., ArcZ, DsrA, and RprA) in and backgrounds, and then artificially regulated the cellular DsrA concentration in these strains by controlling its ectopic expression. We then examined how the expression level of was altered by a change in the concentration of DsrA. We found that the translation and stability of the mRNA are both enhanced by physiological concentrations of DsrA regardless of Hfq, but that depletion of Hfq causes a rapid degradation of DsrA and thereby decreases mRNA stability. These results suggest that the observed Hfq dependency of DsrA-mediated activation mainly results from the destabilization of DsrA in the absence of Hfq, and that DsrA itself contributes to the translational activation and stability of the mRNA in an Hfq-independent manner.