PHOP PHOQ TRANSCRIPTIONAL REPRESSION OF SALMONELLA-TYPHIMURIUM INVASION GENES - EVIDENCE FOR A ROLE IN PROTEIN SECRETION/

Previously, the PhoP-repressed locus prgH was identified as important for signalling epithelial cells to endocytose Salmonella typhimurium. Characterization of prgH revealed that it is an operon of four genes e ncoding polypeptides of 392 (prgH), 80 (prgI), 101 (prgJ) and 252 amin o acid residues (prgK). Synthesis of the 2.6 kb prgHIJK transcript was repressed in bacteria that activate PhoP/PhoQ, indicating that PhoP/P hoQ regulates prgHIJK by transcriptional repression. The prgI, prgJ an d prgK predicted gene products were similar to Shigella flexneri and Y ersinia enterocolitica proteins required for secretion of Ipa and Yop virulence factors. Analysis of the culture supernatants from wild-type S. typhimurium demonstrated that at least 25 polypeptides larger than 14 kDa could be detected. In contrast, prgH1::TnphoA, phoP-constituti ve and hil-deletion mutants had significant defects in their supernata nt protein profiles. The invasion and supernatant protein profile defe cts of the prgH1::TnphoA mutant were both complemented by a 5.1 kb pla smid that included prgHIJK. These results suggest that PhoP/PhoQ regul ates extracellular transport of proteins by transcriptional repression of secretion determinants and that secreted proteins may be involved in signalling epithelial cells to endocytose bacteria.