title: The H-NS protein represses transcription of the eltAB operon, which encodes heat-labile enterotoxin in enterotoxigenic Escherichia coli, by binding to regions downstream of the promoter.
abstract: Heat-labile enterotoxin, a major virulence determinant of enterotoxigenic Escherichia coli, is encoded by the eltAB operon. To elucidate the molecular mechanism by which the heat-stable nucleoid-structural (H-NS) protein controls transcription of eltAB, the authors constructed an eltAB-lacZ transcriptional fusion and performed beta-galactosidase analysis. The results showed that H-NS protein exerts fivefold repression on transcription from the eltAB promoter at 37 degrees C and 10-fold repression at 22 degrees C. Two silencer regions that were required for H-NS-mediated repression of eltAB expression were identified, both of which were located downstream of the start site of transcription. One silencer was located between +31 and +110, the other between +460 and +556, relative to the start site of transcription, and they worked cooperatively in repression. DNA sequences containing the silencers were predicted to be curved by in silico analysis and bound H-NS protein directly in vitro. Repression of eltAB transcription by H-NS was independent of promoter strength, and the presence of H-NS protein did not affect promoter opening in vitro, indicating that repression was achieved by inhibiting promoter clearance or blocking transcription elongation, probably via DNA looping between the two silencers.
authors.affiliation: Department of Microbiology and Immunology, University of Melbourne, Victoria 3010, Australia, and Murdoch Childrens Research Institute, Royal Children's Hospital, Flemington Road, Parkville, Victoria 3052, Australia.
authors.forename: Ji
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Microbiology and Immunology, University of Melbourne, Victoria 3010, Australia, and Murdoch Childrens Research Institute, Royal Children's Hospital, Flemington Road, Parkville, Victoria 3052, Australia.
authors.forename: Marija
authors.initials: M
authors.lastname: Tauschek
authors.affiliation: Department of Microbiology and Immunology, University of Melbourne, Victoria 3010, Australia, and Murdoch Childrens Research Institute, Royal Children's Hospital, Flemington Road, Parkville, Victoria 3052, Australia.
authors.forename: Richard
authors.initials: R
authors.lastname: Strugnell
authors.affiliation: Department of Microbiology and Immunology, University of Melbourne, Victoria 3010, Australia, and Murdoch Childrens Research Institute, Royal Children's Hospital, Flemington Road, Parkville, Victoria 3052, Australia.
authors.forename: Roy M
authors.initials: RM
authors.lastname: Robins-Browne
mesh_terms: D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000378:metabolism*; D001427:Bacterial Toxins / Q000235:genetics*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004768:Enterotoxins / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism* / Q000472:pathogenicity; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism*; D020868:Gene Silencing; D005798:Genes, Bacterial; D007763:Lac Operon; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009876:Operon; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000378:metabolism*; D017384:Sequence Deletion; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; C031908:H-NS protein, bacteria; D012097:Repressor Proteins; C027538:heat-labile enterotoxin, E coli