title: The control of Azorhizobium caulinodans nifA expression by oxygen, ammonia and by the HF-I-like protein, NrfA.
abstract: The control of Azorhizobium caulinodans nifA expression in response to oxygen and ammonia involves FixLJ, FixK, NtrBC, NtrXY and the HF-I-like protein NrfA. The regulation is thus complex and possibly involves post-transcriptional regulation by NrfA. The coding region of nifA was determined using a translational lacZ fusion and by site-directed mutagenesis to identify which of four in frame AUG codons was used. The major NifA protein is translated from the second AUG codon and is predicted to consist of 613 amino acids. Primer extension analysis showed a major transcript starting 34 bp downstream from the anaerobox in wild-type, nifA, rpoN, ntrC and nrfA strains, but not in a fixK mutant. FixK- and oxygen-dependent transcription of nifA was confirmed by the analysis of four transcriptional nifA-lacZ fusions with fusion junctions at positions +1, +47, +110 and +181 with respect to the start site. Regulation by ammonia was independent of FixK and RpoN, NtrC being only partially required. Thus, there may be another type of nitrogen control that does not involve NtrC in A. caulinodans. NrfA is not required for the initiation of nifA transcription but, most probably, has an effect on nifA mRNA stability and/or translation. NrfA also restores the defect in rpoS translation to an Escherichia coli hfq mutant, indicating that HF-I and NrfA have similar activities in both A. caulinodans and E. coli.
authors.affiliation: Unité de Physiologie Cellulaire and URA 1300 CNRS, Département des Biotechnologies, Institut Pasteur, Paris, France. akaminsk@pasteur.fr
authors.forename: P A
authors.initials: PA
authors.lastname: Kaminski
authors.forename: C
authors.initials: C
authors.lastname: Elmerich
mesh_terms: D000595:Amino Acid Sequence; D000641:Ammonia / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D018387:Codon, Initiator; D004268:DNA-Binding Proteins; D012321:DNA-Directed RNA Polymerases / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D016946:Gram-Negative Aerobic Rods and Cocci / Q000235:genetics*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010100:Oxygen / Q000494:pharmacology*; D010957:Plasmids / Q000235:genetics; D011401:Promoter Regions, Genetic; D051877:RNA Polymerase Sigma 54; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017384:Sequence Deletion; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D018387:Codon, Initiator; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C061338:NifA protein, Bacteria; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C087372:nfrA protein, Azorhizobium caulinodans; C497751:rpoN protein, E coli; C069567:sigma factor KatF protein, Bacteria; D000641:Ammonia; D012321:DNA-Directed RNA Polymerases; D051877:RNA Polymerase Sigma 54; D001616:beta-Galactosidase; D010100:Oxygen