Cp. Lostroh et al., The cis requirements for transcriptional activation by HilA, a virulence determinant encoded on SPI-1, MOL MICROB, 37(2), 2000, pp. 300-315
In several models of pathogenesis, Salmonella requires genes encoded on Sal
monella pathogenicity island 1 (SPI-1) for virulence. In Salmonella enteric
a serovar Typhimurium (S. typhimurium), most SPI-1 genes are arranged in op
erons and are co-ordinately regulated in response to environmental signals
via the SPI-1-encoded protein HilA. In order to understand how HilA control
s the transcription of SPI-1 genes, we have analysed the invF and prgH prom
oters. We have reconstituted HilA-dependent activation of both promoters in
Escherichia coli by supplying hilA on a plasmid, strongly suggesting that
HilA acts directly on the promoters. By analysing the HilA-dependent activi
ty of deletions and mutations in P-invF, we identified cis elements necessa
ry for HilA-dependent activation. Through biochemical studies, we have defi
ned a probable HilA-binding sequence in the invF promoter. This 'HilA box'
is intact in the minimal promoter identified through deletion analysis, and
it is disrupted in one class of P-invF mutants that has reduced activation
by HilA. The prgH promoter also contains a HilA box in the same position r
elative to the +1 of transcription. This work is the first to connect HilA-
dependent environmental regulation with a specific sequence in a SPI-1 viru
lence gene promoter.