C. Johnston et al., TRANSCRIPTIONAL ACTIVATION OF SALMONELLA-TYPHIMURIUM INVASION GENES BY A MEMBER OF THE PHOSPHORYLATED RESPONSE-REGULATOR SUPERFAMILY, Molecular microbiology, 22(4), 1996, pp. 715-727
The Salmonella typhimurium PhoP-repressed locus prgHIJK encodes compon
ents of a sec-independent type III secretion apparatus. This apparatus
is composed of at least 17 proteins encoded on a 40 kb pathogenicity
island located at centisome 63 on the S. typhimurium chromosome. The s
ecretion apparatus and some of its targets, SspB, SspC and SspD, are n
ecessary for epithelial cell invasion. The transcription of many invas
ion genes, including prgHIJK, is coordinately activated by HilA, a tra
nscription factor encoded within the pathogenicity island. In this rep
ort we identify sirA, a gene located outside the pathogenicity island
that is essential for induction of prgHIJK and hilA transcription, sir
A encodes a 234-amino-acid protein that is essential for S. typhimuriu
m Ssp (Salmonella secreted protein) secretion and invasion and is simi
lar to response regulators of two-component regulatory systems, sirA-m
utant phenotypes could be suppressed by two DNA clones from unlinked l
oci, designated sirB and sirC, These data suggest that SirA may be pho
sphorylated in response to S. typhimurium sensing a mammalian microenv
ironment. Furthermore, SirA phosphorylation is predicted to initiate a
cascade of transcription-factor synthesis which results in invasion-g
ene transcription, Ssp secretion, and bacterial invasion of epithelia.