title: Regulation of Salmonella enterica pathogenicity island 1 (SPI-1) by the LysR-type regulator LeuO.
abstract: LeuO is a quiescent LysR-type regulator belonging to the H-NS regulon. Activation of leuO transcription represses expression of pathogenicity island 1 (SPI-1) in Salmonella enterica serovar Typhimurium and inhibits invasion of epithelial cells. Loss of HilE suppresses LeuO-mediated downregulation of SPI-1. Activation of leuO transcription reduces the level of HilD protein, and loss of HilE restores the wild type HilD level. Hence, LeuO-mediated downregulation of SPI-1 may involve inhibition of HilD activity by HilE, a view consistent with the fact that HilE is a HilD inhibitor. In vivo analyses using β-galactosidase fusions indicate that LeuO activates hilE transcription. In vitro analyses by slot blotting, electrophoretic mobility shift analysis and DNase I footprinting show that LeuO binds the hilE promoter region. Although residual SPI-1 repression by LeuO is observed in the absence of HilE, the LeuO-HilE-HilD 'pathway' appears to be the major mechanism. Because both leuO and SPI-1 are repressed by H-NS, activation of leuO transcription may provide a backup mechanism for SPI-1 repression under conditions that impair H-NS-mediated silencing.
authors.affiliation: Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Apartado 1095, Sevilla, E-41080, Spain.
authors.forename: Elena
authors.initials: E
authors.lastname: Espinosa
authors.forename: Josep
authors.initials: J
authors.lastname: Casadesús
mesh_terms: D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D018983:DNA Footprinting; D024202:Electrophoretic Mobility Shift Assay; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D044404:Genomic Islands; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000096:biosynthesis* / Q000235:genetics; D012486:Salmonella typhimurium / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism*; D037521:Virulence Factors / Q000235:genetics*; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D037521:Virulence Factors; D001616:beta-Galactosidase