title: Regulatory control of the Escherichia coli O157:H7 lpf1 operon by H-NS and Ler.
abstract: Long polar fimbriae 1 (Lpf1) of Escherichia coli O157:H7 is a tightly regulated adhesin, with H-NS silencing the transcriptional expression of the lpf1 operon while Ler (locus of enterocyte effacement-encoded regulator) acts as an antisilencer. We mapped the minimal regulatory region of lpf1 required for H-NS- and Ler-mediated regulation and found that it is 79% AT rich. Three putative sites for H-NS binding were identified. Two of them, named silencer regulatory sequence 1 (SRS1) and SRS2, are located on a region that covers both of the lpf1 promoters (P1 and P2). The third putative H-NS binding site is located within the lpfA1 gene in a region extending from +258 bp to +545 bp downstream of ATG; however, this site does not seem to play a role in lpfA1 regulation under the conditions tested in this work. Ler was also found to interact with Ler binding sites (LBSs). Ler binding site 1 (LBS1) and LBS2 are located upstream of the two promoters. LBS1 overlaps SRS1, while LBS3 overlaps the P1 promoter and SRS2. Based on the experimental data, we propose that H-NS silences lpf1 expression by binding to both of the SRSs on the promoter region, forming an SRS-H-NS complex that prevents RNA polymerase-mediated transcription. A model of the regulation of the lpfA1 operon of E. coli O157:H7 by H-NS and Ler is discussed.
authors.affiliation: Department of Microbiology and Immunology, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-1070, USA.
authors.forename: Maricarmen
authors.initials: M
authors.lastname: Rojas-López
authors.forename: Margarita M P
authors.initials: MM
authors.lastname: Arenas-Hernández
authors.forename: Abraham
authors.initials: A
authors.lastname: Medrano-López
authors.forename: Claudia F
authors.initials: CF
authors.lastname: Martínez de la Peña
authors.forename: José Luis
authors.initials: JL
authors.lastname: Puente
authors.forename: Ygnacio
authors.initials: Y
authors.lastname: Martínez-Laguna
authors.forename: Alfredo G
authors.initials: AG
authors.lastname: Torres
mesh_terms: D018830:Adhesins, Escherichia coli / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018983:DNA Footprinting; D004269:DNA, Bacterial; D003851:Deoxyribonucleases; D019453:Escherichia coli O157 / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D036781:Fimbriae Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D009154:Mutation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*
chemical_list: D018830:Adhesins, Escherichia coli; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C529458:FimG protein, E coli; C465556:Ler protein, E coli; C571199:LpfA1 protein, E coli; D015534:Trans-Activators; D036781:Fimbriae Proteins; D003851:Deoxyribonucleases