Method for Isolating Mutants Overproducing Nicotinamide Adenine Dinucleotide and Its Precursors

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Abstract
A procedure has been developed for isolating mutants which are defective with respect to nicotinamide adenine dinucleotide (NAD) metabolism. It is based on the well known V-factor requirement of Haemophilus parainfluenzae . This procedure was used to isolate a series of mutants from Escherichia coli . The pyridine metabolism of wild-type and mutant E. coli cells falls in one of four distinct classes. Class A includes wild-type E. coli and represents strains that are normal with respect to pyridine metabolism. Class B mutants have altered internal pools of NAD. The intracellular NAD concentration of different class B mutants varies over a 10-fold range. Class C mutants excrete pyridine mononucleotides, and class D mutants excrete NAD. The production of pyridine nucleotides by class C and D mutants exceeds that of wild-type E. coli by a factor of at least ten. The mutant strains generally have normal generation times and achieve normal cell densities in minimal medium.