Factors affecting increased production of tryptophan synthetase by a TD mutant of Neurospora crassa.

Matchett, William H. (University of California, San Diego, La Jolla, Calif.) and John A. DeMoss. Factors affecting increased production of tryptophan synthetase by a td mutant of Neurospora crassa. J. Bacteriol. 83:1294-1300. 1962.-Mutant td 201 of Neurospora crassa produces a tryptophan synthetase in significantly larger amount than the parental wild-type strain. Evidence obtained in the present investigation indicates that tryptophan synthetase formation in this mutant is subject to end product regulation by a pool of internal tryptophan. An accelerated rate of formation of enzyme was observed when the level of internal tryptophan fell below the value of 1 mumole per g dry weight of mycelium. It is concluded, therefore, that the high level of enzyme found in this strain results from release of repression. In experiments with the parental wild-type strain, no such release of repression was observed. The significance of these results for the problem concerning the nature of the mutation giving rise to mutant td 201 is discussed. Evidence indicating a marked effect of growth temperature upon metabolism of externally supplied tryptophan is presented.