Salmonella typhimurium mutants lacking NAD pyrophosphatase

NAD can serve as both a purine and a pyridine source for Salmonella typhimurium. Exogenous NAD is rapidly broken down into nicotinamide mononucleotide and AMP by an NAD pyrophosphatase, the first step in the pathway for the assimilation of exogenous NAD. We isolated and characterized mutants of S. typhimurium lacking NAD pyrophosphatase activity; such mutants were identified by their failure to use exogenous NAD as a purine source. These mutants carry mutations that map at a new locus, designated pnuE, between 86 and 87 min on the Salmonella chromosome.