Autoactivation and environmental regulation of bfpT expression, the gene coding for the transcriptional activator of bfpA in enteropathogenic Escherichia coli.
Expression of bfpA, the gene coding for the structural subunit of the bundle-forming pili (BFP) in enteropathogenic Escherichia coli (EPEC), requires the product of bfpT (also called perA), a member of the AraC family of transcriptional regulators. Here, we show that bfpT-cat fusions were not expressed in a bfpT - or in a non-EPEC strain, unless a functional bfpT was present, indicating that an autoregulatory mechanism is involved in expression. Further experiments with bfpT-cat fusions and primer extension analysis showed that bfpT is transcribed from a conventional sigma-70 promoter and that it is expressed throughout the growth curve. It is regulated in response to the ammonium concentration, temperature and growth media, in the same proportions as those described previously for bfpA. In addition, bfpT and bfpA expression was also modulated by osmolarity, but was not affected by pH, iron excess or limitation. Deletion analysis of the bfpT upstream region revealed that a DNA segment of 81 bp, extending upstream from the transcriptional start site, contained all the sequence elements required for maximal expression of bfpT. Furthermore, it shares significant homology with a bfpA upstream AT-rich region, which has been shown to be involved in the BfpT-dependent regulation of bfpA. Interestingly, ammonium repression was observed only when bfpT-cat or bfpA-cat expression was complemented in an EPEC background, whereas low-temperature regulation was observed in both EPEC and non-EPEC strains. This suggests that specific regulatory elements are present in EPEC, while others are shared with non-pathogenic E. coli.
Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca, Morelos 62250, Mexico.
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Martínez-Laguna
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Calva
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D000595:Amino Acid Sequence; D051777:AraC Transcription Factor; D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis / Q000235:genetics; D001426:Bacterial Proteins; D001483:Base Sequence; D003470:Culture Media / Q000494:pharmacology*; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000472:pathogenicity; D029968:Escherichia coli Proteins; D036781:Fimbriae Proteins; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D005798:Genes, Bacterial; D017930:Genes, Reporter; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000494:pharmacology; D008969:Molecular Sequence Data; D005810:Multigene Family; D009994:Osmolar Concentration; D011401:Promoter Regions, Genetic / Q000235:genetics; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012097:Repressor Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D017384:Sequence Deletion; D012689:Sequence Homology, Nucleic Acid; D012808:Sigma Factor / Q000378:metabolism; D013696:Temperature; D014157:Transcription Factors; D014158:Transcription, Genetic / Q000235:genetics*; D014774:Virulence / Q000235:genetics
D051777:AraC Transcription Factor; C497371:AraC protein, E coli; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; C104901:BfpA protein, E coli; D003470:Culture Media; D029968:Escherichia coli Proteins; D000644:Quaternary Ammonium Compounds; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C120886:bfpT protein, E coli; D036781:Fimbriae Proteins; D007501:Iron; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases