Regulation mechanism of HilDC-dependent invF expression in Salmonella pathogenicity island 1

Abstract

During infection to its host, Salmonella enterica serovar Typhimurium enters the epithelial cells of the small intestine. This process requires a type III secretion system (TTSS) encoded on Salmonella pathogenicity islands 1 (SPI-1), a 40kb stretch of DNA located near 63 cs of chromosome. Four SPI-1 encoded transcriptional regulators, HilD, HilC, HilA and InvF, activate expression of the SPI-1 TTSS. invF has two promoters. One promoter is activated by HilA and the other is activated by HilD/C. Effects of regulators and growth conditions on the expression of invF were examined using primer extension analysis and β-galactosidase assay. HilD/C-dependent invF expression was activated in exponential phase under high-oxygen condition, and it was repressed in stationary phase under low-oxygen condition. HilC or HilD overexpression increased invF expression under both high- and low-oxygen conditions. However, HilD/C dependent invF expression was influenced more by hilD mutation than by hilC mutation. It is also likely that invF is autoregulated. HilA-dependent promoter deleted strain was created by λ red recombination method and invasion assay was performed. In high-oxygen, invasion level was same with wild type, however, in low-oxygen, invasion of mutant was decreased about half level with wild type. Additionally in vivo transcription analysis from invF, hilD, and HilD/C-dependent invF promoter was performed and expressions were increased in invF mutant strain.