title: DNA supercoiling contributes to disconnect sigmaS accumulation from sigmaS-dependent transcription in Escherichia coli.
abstract: The sigmaS subunit of RNA polymerase is a key regulator of Escherichia coli transcription in stress conditions. sigmaS accumulates in cells subjected to stresses such as an osmotic upshift or the entry into stationary phase. We show here that, at elevated osmolarity, sigmaS accumulates long before the beginning of the sigmaS-dependent induction of osmEp, one of its target promoters. A combination of in vivo and in vitro evidence indicates that a high level of DNA negative supercoiling inhibits transcription by EsigmaS. The variations in superhelical densities occurring as a function of growth conditions can modulate transcription of a subset of sigmaS targets and thereby contribute to the temporal disconnection between the accumulation of sigmaS and sigmaS-driven transcription. We propose that, in stress conditions leading to the accumulation of sigmaS without lowering the growth rate, the level of DNA supercoiling acts as a checkpoint that delays the shift from the major (Esigma70) to the general stress (EsigmaS) transcriptional machinery, retarding the induction of a subset of the sigmaS regulon until the conditions become unfavourable enough to cause entry into stationary phase.
authors.affiliation: Laboratoire de Microbiologie et Génétique Moléculaire, UMR 5100 CNRS - Université Toulouse III, France.
authors.forename: Patricia
authors.initials: P
authors.lastname: Bordes
authors.forename: Annie
authors.initials: A
authors.lastname: Conter
authors.forename: Violette
authors.initials: V
authors.lastname: Morales
authors.forename: Jean
authors.initials: J
authors.lastname: Bouvier
authors.forename: Annie
authors.initials: A
authors.lastname: Kolb
authors.forename: Claude
authors.initials: C
authors.lastname: Gutierrez
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism*; D004278:DNA, Superhelical / Q000737:chemistry / Q000378:metabolism*; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics; D005786:Gene Expression Regulation; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D008565:Membrane Proteins / Q000235:genetics; D009675:Novobiocin / Q000378:metabolism; D009690:Nucleic Acid Conformation; D009994:Osmolar Concentration; D010957:Plasmids / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012808:Sigma Factor / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004278:DNA, Superhelical; D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; C095975:OsmE protein, E coli; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; D009675:Novobiocin; D012321:DNA-Directed RNA Polymerases