The cis requirements for transcriptional activation by HilA, a virulence determinant encoded on SPI‐1

Abstract

In several models of pathogenesis, Salmonella requires genes encoded on Salmonella pathogenicity island 1 (SPI‐1) for virulence. In Salmonella enterica serovar Typhimurium (S. typhimurium), most SPI‐1 genes are arranged in operons and are co‐ordinately regulated in response to environmental signals via the SPI‐1‐encoded protein HilA. In order to understand how HilA controls the transcription of SPI‐1 genes, we have analysed the invF and prgH promoters. 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 activity of deletions and mutations in PinvF, we identified cis elements necessary for HilA‐dependent activation. Through biochemical studies, we have defined 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 PinvF mutants that has reduced activation by HilA. The prgH promoter also contains a HilA box in the same position relative to the +1 of transcription. This work is the first to connect HilA‐dependent environmental regulation with a specific sequence in a SPI‐1 virulence gene promoter.

Regulation ofSalmonella entericaPathogenicity Island 1 by DNA Adenine Methylation

“…Only those regulators that are known to control a specific SPI-1 transcriptional unit were included in the analysis. For instance, expression of hilC in the absence of HilA was not tested because hilC is not regulated by hilA (Rakeman et al 1999;Lostroh et al 2000). In turn, expression of the hilA in the absence of InvF was omitted because InvF is downstream from HilA in the SPI-1 regulatory cascade (Figure 1).…”

DNA-Binding Activities of the HilC and HilD Virulence Regulatory Proteins ofSalmonella entericaSerovar Typhimurium

“…Many regulatory proteins influence invasion gene expression (31,32), but the key regulator is the SPI1-encoded HilA protein, which can activate their transcription directly (1,4,28) or by increasing expression of the activator InvF (9). The N-terminal region of HilA carries a DNA-binding and transcription-activating helix-loop-helix motif typical of OmpR/ToxR family members (4).…”

Detection of hilA gene sequences in serovars of Salmonella enterica sufigbspecies enterica

“…Several genes have been identified and associate with the complex mechanisms that S. enterica serovar Typhimurium uses to invade epithelial intestinal cells (Darwin & Miller 1999, Lostroh et al 2000, Detweiler et al 2001, Lucas & Lee 2001. Salmonella Pathogenicity Island 1 (SPI1) is composed by several genes, hilA (hyperinvasive locus A), is one of them (Lee 1994, 1996, Lee et al 1992, Bajaj et al 1995, Lostroh et al 2000, Milrod et al 2001 and it is required for the regulation of the type III secretion genes (Lostroh et al 2000, Lesnick et al 2001.…”

“…Salmonella Pathogenicity Island 1 (SPI1) is composed by several genes, hilA (hyperinvasive locus A), is one of them (Lee 1994, 1996, Lee et al 1992, Bajaj et al 1995, Lostroh et al 2000, Milrod et al 2001 and it is required for the regulation of the type III secretion genes (Lostroh et al 2000, Lesnick et al 2001. Virulence genes like type III secretion apparatus, secret proteins that are probably related to cell invasion (Kubori et al 1998, Darwin & Miller 2001, Lesnick et al 2001.…”