LcrQ/YscM1, regulators of the Yersinia yop virulon, are injected into hostcells by a chaperone-dependent mechanism

Pathogenic Yersinia species employ type III machines to secrete YopBDR into the extracellular milieu. After attaching to host cells, yersiniae transfo rm the type III machinery into an injection device and target YopEHMNOPT in to eukaryotic cells. Yersinia pseudotuberculosis LcrQ is a transcriptional regulator that prevents the expression of yop genes. We report that LcrQ is injected into eukaryotic cells. YscM1, the transciptional regulator of Yer sinia enterocolitica, is also injected into eukaryotic cells, whereas the r elated YscM2 protein remains associated with bacterial cells. Type III targ eting of YscM1 requires binding to the SycH chaperone. Chaperone binding as well as depletion of YscM1 and YscM2 from the cytoplasm of Y. enterocoliti ca causes an increase in yop expression, whereas a block in regulator expor t reduces expression. We propose a model whereby the chaperone-mediated inj ection of LcrQ/YscM1 functions as a regulatory switch for bacteria that are attached to host cells, triggering the expression of Yops that travel the type III targeting pathway.