title: Ammonium repression of the nitrite-nitrate (nasAB) assimilatory operon of Azotobacter vinelandii is enhanced in mutants expressing the nifO gene at high levels.
abstract: A number of Tn5 mutants were isolated which were unable to fix nitrogen and showed enhanced ammonium repression of the nitrate/nitrite assimilation genes. They also had reduced nitrate reductase activity under fully inducing conditions. Insertions were localized within the nifB gene, and inability to fix nitrogen was shown to be due to disruption of the nifB gene. However, enhanced ammonium repression proved to be the result of constitutive expression of the downstream nifO gene from an 'out' promoter present in Tn5. Our results suggest that molybdenum metabolism might function as a regulatory factor that acts through the nitrate reductase.
authors.affiliation: Departamento de Microbiologia, Faculdad de Biologia, Universidad de Sevilla, Spain.
authors.forename: J C
authors.initials: JC
authors.lastname: Gutierrez
authors.forename: E
authors.initials: E
authors.lastname: Santero
authors.forename: M
authors.initials: M
authors.lastname: Tortolero
mesh_terms: D016948:Azotobacter vinelandii / Q000187:drug effects / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics; D002704:Chlorates / Q000494:pharmacology; D002874:Chromosome Mapping; D002876:Chromosomes, Bacterial; D004251:DNA Transposable Elements; D004352:Drug Resistance, Microbial / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D009154:Mutation; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000235:genetics*; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D009876:Operon; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D014157:Transcription Factors / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D002704:Chlorates; D004251:DNA Transposable Elements; C092498:NifB protein, Bacteria; C489918:NifQ protein, Azotobacter vinelandii; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D014157:Transcription Factors; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D009584:Nitrogen