Figure 2.

Links between ESRs and regulation of the Ysc-Yop T3SS in Y. pseudotuberculosis. CpxR~P down-regulates genes encoding components of the Ysc-Yop system by binding directly to their promoters. It also inhibits expression of the gene encoding the master positive regulator of the ysc-yop genes, lcrF, by the same mechanism. CpxR~P also represses expression of the genes encoding invasin (inv) and its positive regulator RovA. This further inhibits the function of the Ysc-Yop system by compromising the attachment to host cells that is required for efficient Yop delivery. It is not yet known what drives the phosphorylation of CpxR in this situation. Some evidence supports a role for elevated acetyl phosphate generated by the phosphotransacetylase (Pta)—acetate kinase (AtkA) pathway under as yet unknown metabolic conditions. It is also possible that envelope stress caused by assembly of the Ysc-Yop T3SS is sensed by CpxA, which then phosphorylates CpxR. RpoE has been implicated in positively regulating the Ysc-Yop T3SS although the mechanism remains unexplored. OM, outer membrane; IM, inner (cytoplasmic) membrane.