THE ESCHERICHIA-COLI EFG GENE AND THE RHODOBACTER-CAPSULATUS ADGA GENE CODE FOR NH3-DEPENDENT NAD SYNTHETASE

The essential gene efg, which complements ammonia-dependent growth (ad gA) mutations in Rhodobacter capsulatus and is located at 38.1 min on the Escherichia coli chromosome, was found to code for NH3-dependent N AD synthetase. Crude extracts from a strain which overproduces the efg gene product contained up to 400 times more activity than crude extra cts from the control strain, and the purified Efg protein possessed NH 3-dependent NAD synthetase activity. Glutamine-dependent NAD synthetas e activity was found in crude extracts of E. coli but not in the purif ied enzyme, suggesting that it may be catalyzed by an additional subun it. An R. capsulatus strain carrying an adgA mutation was found to be deficient in NAD synthetase activity, and activity was restored by com plementation with the E. coli gene. In accordance with the nomenclatur e proposed for Salmonella typhimurium (K. T. Hughes, B. M. Olivera, an d J. R. Both, J. Bacteriol, 170:2113-2120, 1988), the efg and adgA gen es should now be designated nadE.