title: Bicarbonate-mediated transcriptional activation of divergent operons by the virulence regulatory protein, RegA, from Citrobacter rodentium.
abstract: Regulation of virulence gene expression plays a central role in the pathogenesis of enteric bacteria as they encounter diverse environmental conditions in the gastrointestinal tract of their hosts. In this study, we investigated environmental regulation of two putative virulence determinants adcA and kfc by RegA, an AraC/XylS-like regulator, from Citrobacter rodentium, and identified bicarbonate as the environmental signal which induced transcription of adcA and kfc through RegA. Primer extension experiments showed that adcA and kfc were divergently transcribed from sigma(70) promoters. In vivo and in vitro experiments demonstrated that bicarbonate facilitated and stabilized the binding of RegA to an operator located between the two promoters. The interaction of RegA with its DNA target resulted in the formation of a nucleosome-like structure, which evidently displaced the histone-like proteins, H-NS and StpA, from the adcA and kfc promoter regions, leading to transcriptional derepression. In addition, our results indicated that RegA also behaved as a Class I activator by directly stimulating transcription initiation by RNA polymerase. This is the first report to describe the molecular mechanism by which an environmental chemical stimulates transcription of virulence-associated genes of an enteric pathogen through an AraC/XlyS-like activator.
authors.affiliation: Department of Microbiology and Immunology, The University of Melbourne, Victoria 3010, Australia.
authors.forename: Ji
authors.initials: J
authors.lastname: Yang
authors.forename: Emily
authors.initials: E
authors.lastname: Hart
authors.forename: Marija
authors.initials: M
authors.lastname: Tauschek
authors.forename: G Dean
authors.initials: GD
authors.lastname: Price
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: Hartland
authors.forename: Richard A
authors.initials: RA
authors.lastname: Strugnell
authors.forename: Roy M
authors.initials: RM
authors.lastname: Robins-Browne
mesh_terms: D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001639:Bicarbonates / Q000378:metabolism*; D044082:Citrobacter rodentium / Q000235:genetics / Q000502:physiology*; D018983:DNA Footprinting; D004269:DNA, Bacterial / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D008969:Molecular Sequence Data; D009707:Nucleosomes / Q000378:metabolism; D009875:Operator Regions, Genetic; D009876:Operon; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D024363:Transcription Initiation Site; D015533:Transcriptional Activation / Q000187:drug effects*; D037521:Virulence Factors / Q000096:biosynthesis*; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D001639:Bicarbonates; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria; D009707:Nucleosomes; C072722:RegA protein, Bacteria; D037521:Virulence Factors; D001616:beta-Galactosidase