title: Regulation of nitrogen fixation in Azorhizobium caulinodans: identification of a fixK-like gene, a positive regulator of nifA.
abstract: The nucleotide sequence of a 1 kb fragment upstream of Azorhizobium caulinodans fixL was established. An open reading frame of 744 bp was identified as a fixK homologue. A kanamycin cartridge was inserted into the cloned fixK-like gene and recombined into the host genome. The resulting mutant was Nif-Fix-, suggesting that FixK was required for nitrogen fixation both in symbiotic conditions and in the free-living state. Using a pfixK-lacZ fusion, the FixLJ products were shown to control the expression of fixK. Using a pnifA-lacZ fusion, the FixK product was shown to regulate positively the transcription of nifA in bacteria grown in the free-living state. In addition, a double ntrC-fixL mutant was constructed and was shown to be completely devoid of nitrogenase activity. A model of regulation, based on these data, is presented and might explain the unusual ability of A. caulinodans to fix nitrogen both under symbiotic conditions and in the free-living state.
authors.affiliation: Unité de Physiologie Cellulaire, Institut Pasteur, Paris, France.
authors.forename: P A
authors.initials: PA
authors.lastname: Kaminski
authors.forename: K
authors.initials: K
authors.lastname: Mandon
authors.forename: F
authors.initials: F
authors.lastname: Arigoni
authors.forename: N
authors.initials: N
authors.lastname: Desnoues
authors.forename: C
authors.initials: C
authors.lastname: Elmerich
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D004352:Drug Resistance, Microbial / Q000235:genetics; D004926:Escherichia coli / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D005798:Genes, Bacterial; D007612:Kanamycin / Q000494:pharmacology; D007700:Kinetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation / Q000235:genetics; D009591:Nitrogenase / Q000235:genetics; D016366:Open Reading Frames / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012230:Rhizobiaceae / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C066628:FixK protein, Bacteria; D007612:Kanamycin; D009591:Nitrogenase; D001616:beta-Galactosidase; D009584:Nitrogen