title: The H-NS-like protein HvrA modulates expression of nitrogen fixation genes in the phototrophic purple bacterium Rhodobacter capsulatus by binding to selected nif promoters.
abstract: Genetic analyses based on chromosomal lac fusions to nitrogen fixation (nif) genes demonstrated that NifA-dependent transcriptional activation of expression of Rhodobacter capsulatus nifH and nifB1 was negatively modulated by HvrA, whereas regulation of rpoN, nifA1, and nifA2 was independent of HvrA. Expression of hvrA itself was not influenced by a mutation in ntrC, which is absolutely essential for N(2) fixation. Furthermore, HvrA accumulated to comparable levels in the presence and absence of ammonium, suggesting that the amount of HvrA in the cells does not differ under nitrogenase-repressing or -derepressing conditions. In addition, competitive gel retardation studies with HvrA-His(6) purified from R. capsulatus were carried out, demonstrating preferential binding of HvrA to the nifH promoter region.
authors.affiliation: Ruhr-Universität Bochum, Fakultät für Biologie, Lehrstuhl für Biologie der Mikroorganismen, 44780, Bochum, Germany.
authors.forename: Karsten
authors.initials: K
authors.lastname: Raabe
authors.forename: Thomas
authors.initials: T
authors.lastname: Drepper
authors.forename: Kai Uwe
authors.initials: KU
authors.lastname: Riedel
authors.forename: Bernd
authors.initials: B
authors.lastname: Masepohl
authors.forename: Werner
authors.initials: W
authors.lastname: Klipp
mesh_terms: D001426:Bacterial Proteins / Q000502:physiology*; D015153:Blotting, Western; D004268:DNA-Binding Proteins; D024202:Electrophoretic Mobility Shift Assay; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D009586:Nitrogen Fixation / Q000235:genetics*; D009591:Nitrogenase / Q000235:genetics / Q000502:physiology; D010088:Oxidoreductases; D051922:PII Nitrogen Regulatory Proteins; D011401:Promoter Regions, Genetic; D016354:Rhodobacter capsulatus / Q000187:drug effects / Q000235:genetics*; D015534:Trans-Activators / Q000502:physiology*; D014157:Transcription Factors; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria; C090405:HvrA protein, Rhodobacter capsulatus; D051922:PII Nitrogen Regulatory Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D010088:Oxidoreductases; D009591:Nitrogenase; C029130:nitrogenase reductase; D001616:beta-Galactosidase