The Azorhizobium caulinodans nitrogen-fixation regulatory gene, nifA, is controlled by the cellular nitrogen and oxygen status.
The nucleotide sequence of the Azorhizobium caulinodans ORS571 nifA locus was determined and the deduced NifA amino acid sequence compared with that of NifA from other nitrogen-fixing species. Highly conserved domains, including helix-turn-helix and ATP-binding motifs, and specific conserved residues, such as a cluster of cysteines, were identified. The nifA 5' upstream region was found to contain DNA sequence motifs highly homologous to promoter elements involved in nifA/ntr-mediated control and a consensus element found in the 5' upstream region of the Bradyrhizobium japonicum 5-aminolevulinic acid synthase (hemA) gene and of Escherichia coli genes activated during anaerobiosis via the fnr (fumarate nitrate reduction) control system. A nifA-lac fusion was constructed using miniMu-lac and its activity measured in different genetic backgrounds and under various physiological conditions (in culture and in planta). NifA expression was found to be negatively autoregulated, repressed by rich nitrogen sources and high oxygen concentrations, and controlled (partially) by the ntrC gene, both in culture and in planta. DNA supercoiling was also implicated in nifA regulation, since DNA gyrase inhibitors severely repressed nifA-lac expression.
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Max-Planck-Institut für Züchtungsforschung, Abteilung Genetische Grundlagen der Pflanzenzüchtung, Köln, FRG.
Pawlowski
K
K
Schell
J
J
de Bruijn
F J
FJ
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D005786:Gene Expression Regulation; D005798:Genes, Bacterial; D007711:Klebsiella pneumoniae / Q000235:genetics; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000235:genetics*; D010100:Oxygen / Q000378:metabolism*; D010641:Phenotype; D011401:Promoter Regions, Genetic; D015183:Restriction Mapping; D012230:Rhizobiaceae / Q000235:genetics* / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic
D009584:Nitrogen; D010100:Oxygen