Role of the nac gene product in the nitrogen regulation of some NTR-regulated operons of Klebsiella aerogenes.
A positive, genetic selection against the activity of the nitrogen regulatory (NTR) system was used to isolate insertion mutations affecting nitrogen regulation in Klebsiella aerogenes. Two classes of mutation were obtained: those affecting the NTR system itself and leading to the loss of almost all nitrogen regulation, and those affecting the nac locus and leading to a loss of nitrogen regulation of a family of nitrogen-regulated enzymes. The set of these nac-dependent enzymes included histidase, glutamate dehydrogenase, glutamate synthase, proline oxidase, and urease. The enzymes shown to be nac independent included glutamine synthetase, asparaginase, tryptophan permease, nitrate reductase, the product of the nifLA operon, and perhaps nitrite reductase. The expression of the nac gene was itself highly nitrogen regulated, and this regulation was mediated by the NTR system. The loss of nitrogen regulation was found in each of the four insertion mutants studied, showing that loss of nitrogen regulation resulted from the absence of nac function rather than from an altered form of the nac gene product. Thus we propose two classes of nitrogen-regulated operons: in class I, the NTR system directly activates expression of the operon; in class II, the NTR system activates nac expression and the product(s) of the nac locus activates expression of the operon.
Macaluso
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Department of Biology, University of Michigan, Ann Arbor 48109.
Best
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Bender
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D026905:Amino Acid Transport Systems; D001215:Asparaginase / Q000378:metabolism; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D005969:Glutamate Dehydrogenase / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D006638:Histidine Ammonia-Lyase / Q000378:metabolism; D007711:Klebsiella pneumoniae / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism; D009154:Mutation; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism; D009584:Nitrogen / Q000502:physiology*; D009876:Operon; D029701:Saccharomyces cerevisiae Proteins; D012808:Sigma Factor / Q000502:physiology; D014510:Urease / Q000378:metabolism; D001616:beta-Galactosidase / Q000378:metabolism
D026905:Amino Acid Transport Systems; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; D012808:Sigma Factor; C429825:TAT2 protein, S cerevisiae; C035131:TnaB protein, E coli; D005969:Glutamate Dehydrogenase; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D001616:beta-Galactosidase; D001215:Asparaginase; D014510:Urease; D006638:Histidine Ammonia-Lyase; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen