Differential activation of the tcpPH promoter by AphB determines biotype specificity of virulence gene expression in Vibrio cholerae.
Vibrio cholerae strains of the classical biotype express the genes encoding cholera toxin (CT) and toxin-coregulated pilus (TCP) under a variety of environmental conditions in vitro, whereas El Tor biotype strains express these genes only under specialized culture conditions. We show here that a single base-pair difference at positions -65 and -66 of the classical and El Tor tcpPH promoters, respectively, is responsible for the differential regulation of virulence gene expression in these two disease-causing biotypes. Analysis of tcpP-lacZ fusions in both V. cholerae and Escherichia coli indicated that transcriptional activation of the El Tor tcpPH promoter by the LysR regulator AphB was significantly reduced relative to that of the classical promoter. Reciprocal exchange of the tcpPH promoter between the two biotypes in V. cholerae showed that the ability to activate the transcription of tcpPH is not dependent on the biotype of the strain per se but on the tcpPH promoter itself. Classical and El Tor tcpP-lacZ promoter chimeras in E. coli localized the region responsible for the differential activation of tcpPH by AphB to within 75 bp of the transcriptional start site. Individual base-pair changes within this region showed that the presence of either an A or a G at position -65 or -66 conferred the classical or El Tor, respectively, pattern of tcpPH activation by AphB. Reciprocal exchange of these base pairs between biotypes in V. cholerae switched the biotype-specific pattern of expression of tcpPH as well as the production of CT and TCP in response to environmental stimuli.
Kovacikova
G
G
Department of Microbiology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Skorupski
K
K
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics; D036781:Fimbriae Proteins; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D007763:Lac Operon; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D013045:Species Specificity; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors; D014734:Vibrio cholerae / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity*
C120327:AphB protein, Vibrio cholerae; D001426:Bacterial Proteins; D011993:Recombinant Fusion Proteins; C097244:TCPP protein, Vibrio cholerae; C099204:TcpH protein, Vibrio cholerae; D015534:Trans-Activators; D014157:Transcription Factors; D036781:Fimbriae Proteins