SUMMARY: is inhibited by the analogue of phenylalanine, -fluorophenyl-alanine (FPA). Mutant strain f7, selected for growth on FPA, is a slow grower which is not inhibited by the analogue. Over a prolonged period of growth, the amount of [C]FPA incorporated into the trichloroacetic acid-insoluble fraction of resistant f7 mycelium is significant, but is less than 20% of the amount incorporated into similar fractions of the mycelium of the parental sensitive strain tci. Resistant f7, grown on minimal medium, excretes into the medium -hydroxy-phenylpyruvic acid, phenylpyruvic acid and a number of unidentified phenolic compounds. The sensitive tci strain grown on minimal medium does not excrete, but when grown on media supplemented with phenylalanine or shikimate excretes traces of these compounds. The total biosynthesis of phenylalanine over 24 h by sensitive strain tci is greatly reduced by the presence of exogenously supplied phenylalanine. No such reduction in synthesis is observed in the resistant mutant f7. It is inferred that the mutation impairs the regulation of phenylalanine biosynthesis, probably by the loss of feedback control at either the 3-deoxy-d--heptulo-sonate 7-phosphate (DAHP) synthetase or chorismate mutase.


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