A regulatory network controls expression of the in vivo-expressed HreP protease of Yersinia enterocolitica.

The human enteropathogen Yersinia enterocolitica survives and replicates in the lymphoid tissues of its host. Previous in vivo analyses of gene expression revealed that various chromosomal genes are expressed at this stage of infection, but not in vitro. One of these, termed hreP, encodes a protease that is necessary for full virulence of Y. enterocolitica. Using transposon mutagenesis, we identified three genes, pypA, pypB, and pypC, as positive regulators of hreP transcription. PypA is an inner membrane protein with no significant similarity to any known proteins; PypB is a ToxR-like transmembrane transcriptional regulator; and PypC is a cytoplasmic transcriptional regulator with an OmpR-like winged helix-turn-helix DNA binding motif. We show that all Pyp proteins are able to activate hreP independently of each other and that PypB and PypC interact directly with the hreP promoter region. Furthermore, pypB and pypC are autoregulated and regulate each other. Additional data indicate that transcription of hreP is repressed by the histone-like nucleoid-structuring protein H-NS in a temperature-dependent manner. Our data reveal a new regulatory network that might have implications for the controlled expression of further virulence-associated functions in Yersinia.