title: Phase variation of Ag43 is independent of the oxidation state of OxyR.
abstract: OxyR is a DNA binding protein that differentially regulates a cell's response to hydrogen peroxide-mediated oxidative stress. We previously reported that the reduced form of OxyR is sufficient for repression of transcription of agn43 from unmethylated template DNA, which is essential for deoxyadenosine methylase (Dam)- and OxyR-dependent phase variation of agn43. Here we provide evidence that the oxidized form of OxyR [OxyR(ox)] also represses agn43 transcription. In vivo, we found that exogenous addition of hydrogen peroxide, sufficient to oxidize OxyR, did not affect the expression of agn43. OxyR(ox) repressed in vitro transcription but only from an unmethylated agn43 template. The -10 sequence of the promoter and three Dam target sequences were protected in an in vitro DNase I footprint assay by OxyR(ox). Furthermore, OxyR(ox) bound to the agn43 regulatory region DNA with an affinity similar to that for the regulatory regions of katG and oxyS, which are activated by OxyR(ox), indicating that binding at agn43 can occur at biologically relevant concentrations. OxyR-dependent regulation of Ag43 expression is therefore unusual in firstly that OxyR binding at agn43 is dependent on the methylation state of Dam target sequences in its binding site and secondly that OxyR-dependent repression appears to be independent of hydrogen-peroxide mediated oxidative stress and the oxidation state of OxyR.
authors.affiliation: Department of Microbiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Anu
authors.initials: A
authors.lastname: Wallecha
authors.forename: Jason
authors.initials: J
authors.lastname: Correnti
authors.forename: Vincent
authors.initials: V
authors.lastname: Munster
authors.forename: Marjan
authors.initials: M
authors.lastname: van der Woude
mesh_terms: D018829:Adhesins, Bacterial; D018830:Adhesins, Escherichia coli; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins; D001665:Binding Sites; D018983:DNA Footprinting / Q000379:methods; D019175:DNA Methylation; D004269:DNA, Bacterial / Q000378:metabolism; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009154:Mutation; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010544:Peroxidases / Q000235:genetics / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D058727:RNA, Small Untranslated
chemical_list: D018829:Adhesins, Bacterial; D018830:Adhesins, Escherichia coli; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D006861:Hydrogen Peroxide; D010544:Peroxidases; D012097:Repressor Proteins; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); D014157:Transcription Factors; C118376:antigen 43, E coli; C499686:oxyS small RNA, E coli; D058727:RNA, Small Untranslated; C076136:catalase HPI; C058693:Dam methyltransferase