EMBO Journal, 13 November 2013, Vol.32(22), pp.2963-2979
Small RNAs use a diversity of well‐characterized mechanisms to repress mRNAs, but how they activate gene expression at the mRNA level remains not well understood. The predominant activation mechanism of Hfq‐associated small RNAs has been translational control whereby base pairing with the target prevents the formation of an intrinsic inhibitory structure in the mRNA and promotes translation initiation. Here, we report a translation‐independent mechanism whereby the small RNA RydC selectively activates the longer of two isoforms of mRNA (encoding cyclopropane fatty acid synthase) in . Target activation is achieved through seed pairing of the pseudoknot‐exposed, conserved 5′ end of RydC to an upstream region of the mRNA. The seed pairing stabilizes the messenger, likely by interfering directly with RNase E‐mediated decay in the 5′ untranslated region. Intriguingly, this mechanism is generic such that the activation is equally achieved by seed pairing of unrelated small RNAs, suggesting that this mechanism may be utilized in the design of RNA‐controlled synthetic circuits. Physiologically, RydC is the first small RNA known to regulate membrane stability. The small RNA RydC stabilizes target mRNAs in a translation‐independent manner through base pairing to the 5′UTR, blocking RNase E access. Cyclopropane fatty acid synthase is a target for RydC, providing the first link between sRNA regulation and membrane biosynthesis in bacteria.
Fatty Acid Synthesis ; Hfq ; Mrna Activation ; Noncoding Rna ; Small Rna