The biosynthesis of nicotinamide adenine dinucleotide (NAD) is under the genetic control of the nadR+ locus. The nadR+ allele is dominant to the nadR allele in transheterogenotes, indicating that the regulation is of the positive type. Mutants of the nadR type are unable to synthesize quinolinic acid; however, they do retain the ability to convert quinolinic acid into NAD and to recycle this NAD through the pyridine nucleotide cycle. Thus, the nadR+ locus regulates only genes involved in the biosynthesis of quinolinic acid.
De Novo Biosynthesis of Nicotinamide Adenine Dinucleotide in Escherichia coli: Excretion of Quinolinic Acid by Mutants Lacking Quinolinate Phosphoribosyl Transferase1