title: Independent regulation of H-NS-mediated silencing of the bgl operon at two levels: upstream by BglJ and LeuO and downstream by DnaKJ.
abstract: Silencing of the Escherichia coli bgl operon by the histone-like nucleoid-structuring protein H-NS occurs at two levels. Binding of H-NS upstream of the promoter represses transcription initiation, whilst binding within the coding region is also proposed to repress transcription elongation. The latter, downstream level of repression is counteracted by the protease Lon and, thus, silencing of the bgl operon is more effective in lon mutants. Transposon-mutagenesis screens for suppression of this lon phenotype on bgl were performed and insertion mutations disrupting rpoS and crl were obtained, as well as mutations mapping upstream of the open reading frames of bglJ, leuO and dnaK. In rpoS and crl mutants, bgl promoter activity is known to be higher. Likewise, as shown here, bgl promoter activity is increased in the bglJ and leuO mutants, which express BglJ and LeuO constitutively. However, BglJ and LeuO have no impact on downstream repression. A dnaKJ mutant was isolated for the first time in the context of the bgl operon. The mutant expresses lower levels of DnaK than the wild-type. Interestingly, in this dnaKJ : : miniTn10 mutant, downstream repression of bgl by H-NS is less effective, whilst upstream repression by H-NS remains unaffected. Together, the data show that the two levels of bgl silencing by H-NS are regulated independently.
authors.affiliation: Institute for Genetics, University of Cologne, Zülpicherstr. 47, 50674 Cologne, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Madhusudan
authors.affiliation: Institute for Genetics, University of Cologne, Zülpicherstr. 47, 50674 Cologne, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Paukner
authors.affiliation: Institute for Genetics, University of Cologne, Zülpicherstr. 47, 50674 Cologne, Germany.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Klingen
authors.affiliation: Institute for Genetics, University of Cologne, Zülpicherstr. 47, 50674 Cologne, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Schnetz
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D020868:Gene Silencing; D005960:Glucosides / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D016254:Mutagenesis, Insertional; D009876:Operon; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C103411:BglJ protein, E coli; D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D005960:Glucosides; C031908:H-NS protein, bacteria; D018840:HSP70 Heat-Shock Proteins; C430340:LeuO protein, E coli; D015534:Trans-Activators; D014157:Transcription Factors; C063842:dnaK protein, E coli