Staphylococcus aureus RNAIII Binds to Two Distant Regions of coa mRNA to Arrest Translation and Promote mRNA Degradation

Abstract

Staphylococcus aureus RNAIII is the intracellular effector of the quorum sensing system that temporally controls a large number of virulence factors including exoproteins and cell-wall-associated proteins. Staphylocoagulase is one major virulence factor, which promotes clotting of human plasma. Like the major cell surface protein A, the expression of staphylocoagulase is strongly repressed by the quorum sensing system at the post-exponential growth phase. Here we used a combination of approaches in vivo and in vitro to analyze the mechanism used by RNAIII to regulate the expression of staphylocoagulase. Our data show that RNAIII represses the synthesis of the protein through a direct binding with the mRNA. Structure mapping shows that two distant regions of RNAIII interact with coa mRNA and that the mRNA harbors a conserved signature as found in other RNAIII-target mRNAs. The resulting complex is composed of an imperfect duplex masking the Shine-Dalgarno sequence of coa mRNA and of a loop-loop interaction occurring downstream in the coding region. The imperfect duplex is sufficient to prevent the formation of the ribosomal initiation complex and to repress the expression of a reporter gene in vivo. In addition, the double-strand-specific endoribonuclease III cleaves the two regions of the mRNA bound to RNAIII that may contribute to the degradation of the repressed mRNA. This study validates another direct target of RNAIII that plays a role in virulence. It also illustrates the diversity of RNAIII-mRNA topologies and how these multiple RNAIII-mRNA interactions would mediate virulence regulation.

RNAIII of the Staphylococcus aureus agr system activates global regulator MgrA by stabilizing mRNA

“…We provide several lines of evidence supporting this conclusion. RNAIII, as a regulatory effector of the agr system, has so far been shown to affect its target genes at the translational level by RNA base pairing that either masks or unmasks the translation initiation site (10,11,13,14). To our knowledge, the findings presented here are the first to show that S. aureus RNAIII affects a target gene by mRNA stabilization.…”

“…RNAIII is capable of forming a stable structure that is characterized by 14 stem-loop motifs and three long-distance interacting helices (9). Several examples of regulation by direct interaction between RNAIII and its target mRNAs have been reported (10)(11)(12)(13)(14). A common denominator in these regulatory interactions is the targeting of translation initiation sequences, through base pairing of the CU-rich loop domains of RNAIII with regions containing the Shine and Dalgarno (SD) sequence or AUG start codon of the target mRNA, resulting in negative control of translation (15,16).…”

The importance of regulatory RNAs in Staphylococcus aureus

“…This motif is often used to bind the G-rich sequences of the ribosome binding sites of mRNAs. The duplexes formed between the RNAIII and the targeted mRNAs prevent ribosome binding and recruit the double-strand specific RNase III, which initiates the rapid degradation of both the mRNAs and the RNAIII (Boisset et al, 2007;Chevalier et al, 2010;Huntzinger et al, 2005). These mRNAs encode virulence factors expressed at the surface of the cell (protein A, coagulase, SA1000), and the transcriptional repressor of toxins, Rot.…”

RNA folding in living cells

“…[106][107][108][109][110] Similarly, in S. aureus the quorum sensing RNAIII interacts with the transcriptional regulator rot, among others. 111,112 Upon interaction the RBS of the rot mRNA becomes inaccessible, thereby ©2 0 1 1 L a n d e s B i o s c i e n c e .…”