Structural homologues P(II) and P(Z) of Azospirillum brasilense provide intracellular signalling for selective regulation of various nitrogen-dependent functions.
P(II) (glnB) is a signal transduction protein that in Azospirillum brasilense is specifically required for nitrogen fixation. Little is known about whether and how its homologue P(Z) (glnZ) participates in the regulation of cellular functions. In this study, we have shown the regulatory action of the two proteins by analysing the relevant single and double null-mutant strains. The transcription of glnZ is monocistronic, and it starts mainly from a sigma54-dependent promoter, activated by NtrC. glnZ expression is dependent on the ntr system, even under conditions of nitrogen excess, and is greatly enhanced in the presence of aspartate. P(Z) is uridylylated in response to nitrogen limitation, like P(II), although different amounts of the two proteins are synthesized. P(II) is required for the dephosphorylation of NtrC. Thus, in the absence of P(II), the repression of nitrate assimilation is not promoted, which, in turn, leads to a high rate of ammonium excretion. Unexpectedly, P(II) and P(Z) proteins are not essential for the reversible modification of glutamine synthetase. (Methyl)ammonium transport into the cell is negatively regulated by P(Z). The growth of a double-mutant strain (glnB::kan; glnZ::omega) is drastically disabled, although wild-type growth is restored by complementation with either glnB or glnZ. We conclude that P(II) and P(Z), despite their structural similarity, are involved in different regulatory processes, except for that required for cell growth.
Unité de Physiologie Cellulaire (CNRS URA 1300), Département des Biotechnologies, Institut Pasteur, Paris, France. zamaroczy@ibpc.fr
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D000595:Amino Acid Sequence; D015806:Azospirillum brasilense / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D001692:Biological Transport; D015964:Gene Expression Regulation, Bacterial; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D008744:Methylamines / Q000493:pharmacokinetics; D008969:Molecular Sequence Data; D009154:Mutation; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D051922:PII Nitrogen Regulatory Proteins; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014158:Transcription, Genetic
D001426:Bacterial Proteins; C100965:GlnZ protein, Azospirillum brasilense; D008744:Methylamines; D009566:Nitrates; D051922:PII Nitrogen Regulatory Proteins; D000644:Quaternary Ammonium Compounds; C404143:PIID regulatory protein, Bacteria; C027451:methylamine; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen