The nac (nitrogen assimilation control) gene from Escherichia coli.
The nitrogen assimilation control gene, nac, was detected in Escherichia coli but not in Salmonella typhimurium by Southern blotting, using a probe from the Klebsiella aerogenes nac (nacK) gene. The E. coli nac gene (nacE) was isolated from a cosmid clone by complementation of a nac mutation in K. aerogenes. nacE was fully functional in this complementation assay. DNA sequence analysis showed considerable divergence between nacE and nacK, with a predicted amino acid sequence identity of only 79% and most of the divergence in the C-terminal half of the protein sequence. The total predicted size of NAC(E) is 305 amino acids, the same as for NAC(K). A null mutation, nac-28, was generated by reverse genetics. Mutants bearing nac-28 have a variety of phenotypes related to nitrogen metabolism, including slower growth on cytosine, faster growth on arginine, and suppression of the failure of an Ntr-constitutive mutant to grow with serine as sole nitrogen source. In addition to a loss of nitrogen regulation of histidase formation, nac-28 mutants also showed a loss of a weak repression of glutamate dehydrogenase formation. This repression was unexpected because it is balanced by a NAC-independent activation of glutamate dehydrogenase formation during nitrogen-limited growth. Attempts to purify NAC(E) by using methods established for NAC(K) failed, and NAC(E) appears to be degraded with a half-life at 30 degrees C as short as 15 min during inhibition of protein synthesis.
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Department of Biology, The University of Michigan, Ann Arbor 48109-1048, USA. rbender@umich.edu
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D001120:Arginine / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D003360:Cosmids; D003596:Cytosine / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D005796:Genes; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D005969:Glutamate Dehydrogenase / Q000096:biosynthesis / Q000235:genetics; D006638:Histidine Ammonia-Lyase / Q000096:biosynthesis / Q000235:genetics; D007711:Klebsiella pneumoniae / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012486:Salmonella typhimurium / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C072712:NAC protein, bacteria; C489526:Nac protein, E coli; D014157:Transcription Factors; D003596:Cytosine; D001120:Arginine; D005969:Glutamate Dehydrogenase; D006638:Histidine Ammonia-Lyase; D009584:Nitrogen