Small non-coding RNAs (sRNAs) are emerging regulatory elements in bacteria. The Vibrio cholerae sRNA VrrA has previously been shown to down-regulate outer membrane proteins (OmpA and OmpT) and biofilm matrix protein (RbmC) by base-pairing with the 5' region of the corresponding mRNAs. In this study, we present an additional target of VrrA in V. cholerae, the mRNA coding for the ribosome binding protein Vrp. Vrp is homologous to ribosome-associated inhibitor A (RaiA) of Escherichia coli which facilitates stationary phase survival through ribosome hibernation. We show that VrrA down-regulates Vrp protein synthesis by base-pairing to the 5' region of vrp mRNA and that the regulation requires the RNA chaperone protein, Hfq. We further demonstrate that Vrp is highly expressed during stationary phase growth and associates with the ribosome of V. cholerae. The effect of the Vrp protein in starvation survival is synergistic with that of the VC2530 protein, a homolog of the E. coli hibernation promoting factor HPF, suggesting a combined role for these proteins in ribosome hibernation in V. cholerae. Vrp and VC2530 are important for V. cholerae starvation survival under nutrient deficient conditions. While VC2530 is down-regulated in cells lacking vrrA, mutation of vrp results in VC2530 activation. This is the first report indicating a regulatory role for an sRNA, modulating stationary factors involved in bacterial ribosome hibernation.
Keywords: HPF, hibernation promoting factor; Hfq; IF, initiation factor; RMF, ribosome modulation factor; RaiA, ribosome-associated inhibitor A; Ribosome hibernation; SRA, stationary-phase-induced-ribosome associated protein; Vibrio cholerae; Vrp; Vrp, VrrA-regulated ribosome binding protein; VrrA; sRNA.