Posttranscriptional regulation of the virulence regulator LcrF in Yersinia pseudotuberculosis

Yersinia pseudotuberculosis is an enteropathogenic bacterium causing gut-associated diseases. It is taken up by ingestion of contaminated food or water. In the ileum the bacterium crosses the intestinal barrier through the M-cells. After transmigration the adhesin YadA and the Yersinia outer proteins (Yops) enable the bacterium to circumvent the host immune system and to colonize within deeper tissues of the host. These virulence factors are encoded on the virulence plasmid pYV and synthesized only at 37°C. Temperature dependency is thereby mediated by the master regulator LcrF, a member of the AraC-like transcriptional activators. lcrF is organized in an operon together with the upstream encoded virG gene on pYV.

RNA stability assays and primer extension studies show that the polycistronic mRNA of virG and lcrF is rapidly degraded indicating a crucial role of RNA processing in the regulation of lcrF.

Furthermore lcrF translation is under the control of a thermosensitive RNA thermometer. The 5´ UTR of lcrF mRNA forms a secondary structure at 25°C that sequesters the ribosomal binding site. At 37°C this structure melts, ribosomes can bind and translation of lcrF takes place. Point mutations that strengthens respectively loosens the basepairing in the thermosensitive structure show a direct effect on LcrF and YadA production. These mutants have a significant phenotype in mice experiments. This demonstrates for the first time the importance of RNA thermometers on bacterial virulence in an in vivo model.