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J Bacteriol, March 1998, p. 1166-1173, Vol. 180, No. 5
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

The nac (Nitrogen Assimilation Control) Gene from Escherichia coli

Wilson B. Muse and Robert A. Bender*

Department of Biology, The University of Michigan, Ann Arbor, Michigan 48109-1048

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 NACE is 305 amino acids, the same as for NACK. 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 NACE by using methods established for NACK failed, and NACE appears to be degraded with a half-life at 30°C as short as 15 min during inhibition of protein synthesis.

* Corresponding author. Mailing address: Department of Biology, The University of Michigan, Ann Arbor, MI 48109-1048. Phone: (313) 936-2530. Fax: (313) 647-0884. E-mail: rbender{at}umich.edu.




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