title: Integration host factor positively regulates virulence gene expression in Vibrio cholerae.
abstract: Virulence gene expression in Vibrio cholerae is dependent upon a complex transcriptional cascade that is influenced by both specific and global regulators in response to environmental stimuli. Here, we report that the global regulator integration host factor (IHF) positively affects virulence gene expression in V. cholerae. Inactivation of ihfA and ihfB, the genes encoding the IHF subunits, decreased the expression levels of the two main virulence factors tcpA and ctx and prevented toxin-coregulated pilus and cholera toxin production. IHF was found to directly bind to and bend the tcpA promoter region at an IHF consensus site centered at position -162 by using gel mobility shift assays and DNase I footprinting experiments. Deletion or mutation of the tcpA IHF consensus site resulted in the loss of IHF binding and additionally disrupted the binding of the repressor H-NS. DNase I footprinting revealed that H-NS protection overlaps with both the IHF and the ToxT binding sites at the tcpA promoter. In addition, disruption of ihfA in an hns or toxT mutant background had no effect on tcpA expression. These results suggest that IHF may function at the tcpA promoter to alleviate H-NS repression.
authors.affiliation: Department of Microbiology and Immunology, Dartmouth Medical School, Hanover, NH 03755, USA.
authors.forename: Emily
authors.initials: E
authors.lastname: Stonehouse
authors.forename: Gabriela
authors.initials: G
authors.lastname: Kovacikova
authors.forename: Ronald K
authors.initials: RK
authors.lastname: Taylor
authors.forename: Karen
authors.initials: K
authors.lastname: Skorupski
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D036781:Fimbriae Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D015151:Immunoblotting; D034982:Integration Host Factors / Q000235:genetics* / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D011401:Promoter Regions, Genetic / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014734:Vibrio cholerae / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D014774:Virulence / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria; D034982:Integration Host Factors; C085807:TcpA protein, Vibrio cholerae; D014157:Transcription Factors; D036781:Fimbriae Proteins; C075626:tcpN protein, Vibrio cholerae