Phosphoribosyl diphosphate synthetase-independent NAD de novo synthesis in Escherichia coli: a new phenotype of phosphate regulon mutants.
Phosphoribosyl diphosphate-lacking (delta prs) mutant strains of Escherichia coli require NAD, guanosine, uridine, histidine, and tryptophan for growth. NAD is required by phosphoribosyl diphosphate-lacking mutants because of lack of one of the substrates for the quinolinate phosphoribosyltransferase reaction, an enzyme of the NAD de novo pathway. Several NAD-independent mutants of a host from which prs had been deleted were isolated; all of them were shown to have lesions in the pstSCAB-phoU operon, in which mutations lead to derepression of the Pho regulon. In addition NAD-independent growth was dependent on a functional quinolinate phosphoribosyltransferase. The prs suppressor mutations led to the synthesis of a new phosphoryl compound that may act as a precursor for a new NAD biosynthetic pathway. This compound may be synthesized by the product of an unknown phosphate starvation-inducible gene of the Pho regulon because the ability of pst or phoU mutations to suppress the NAD requirement requires PhoB, the transcriptional activator of the Pho regulon.
Department of Biological Chemistry, University of Copenhagen, Denmark.
B
B
Hove-Jensen
D004926:Escherichia coli / Q000378:metabolism*; D009154:Mutation; D009243:NAD / Q000096:biosynthesis*; D009537:Nicotinamide Mononucleotide / Q000378:metabolism; D010641:Phenotype; D010754:Phosphoribosyl Pyrophosphate / Q000172:deficiency; D012268:Ribose-Phosphate Pyrophosphokinase / Q000502:physiology*
D009243:NAD; D009537:Nicotinamide Mononucleotide; D010754:Phosphoribosyl Pyrophosphate; D012268:Ribose-Phosphate Pyrophosphokinase