Salmonella typhimurium nit Is nadE: Defective Nitrogen Utilization and Ammonia-Dependent NAD Synthetase

S. typhimurium nit mutants are defective in nitrogen assimilation, despite having normal levels of assimilatory enzymes. Complementation, enzyme assays, and genetic mapping show that nit is nadE. We present evidence that ammonia, not glutamine, is the physiological substrate for eubacterial NAD synthetases and that low activity completely accounts for the mutant phenotype.