PspG, a New Member of theYersinia enterocoliticaPhage Shock Protein Regulon

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Abstract
TheYersinia enterocoliticaphage shock protein (Psp) system is induced when the Ysc type III secretion system is produced or when only the YscC secretin component is synthesized. Somepspnull mutants have a growth defect when YscC is produced and a severe virulence defect in animals. TheY. enterocolitica psplocus is made up of two divergently transcribed cistrons,pspFandpspABCDycjXF. pspAoperon expression is dependent on RpoN (σ54) and the enhancer-binding protein PspF. Previous data indicated that PspF also controls at least one gene that is not part of thepsplocus. In this study we describe the identification ofpspG, a new member of the PspF regulon. Predicted RpoN-binding sites upstream of thepspAgenes from different bacteria have a common divergence from the consensus sequence, which may be a signature of PspF-dependent promoters. TheY. enterocolitica pspGgene was identified because its promoter also has this signature. Like thepspAoperon,pspGis positively regulated by PspF, negatively regulated by PspA, and induced in response to the production of secretins. Purified His6-PspF protein specifically interacts with thepspAandpspGcontrol regions. ApspAoperon deletion mutant has a growth defect when the YscC secretin is produced and a virulence defect in a mouse model of infection. These phenotypes were exacerbated by apspGnull mutation. Therefore, PspG is the missing component of theY. enterocoliticaPsp regulon that was previously predicted to exist.