Altered Regulatory Mechanisms for Tryptophan Synthesis in Fluorotryptophan-Resistant Mutants of

5-Fluorotryptophan (5FT) inhibited the activity of anthranilate synthetase (AS) of Brevi-bacterium flavum as strongly as did tryptophan. The concentration of 5FT required for complete inhibition of AS was similar to that for growth inhibition. Higher concentrations of 5FT repressed the synthesis of the tryptophan enzymes with a non-coordinate relationship between AS or anthranilate-phosphoribosylpyrophosphate phosphoribosyltransferase (PRT) and indoIe-3-glycerol phosphate synthetase (InGPS) or tryptophan synthetase (TS)-B. In a mutant resistant to low concentrations of 5FT, strain 251, which produced anthranilate and had an AS less sensitive to feedback inhibition by tryptophan, all the tryptophan enzymes showed normal levels. On the other hand, in a mutant resistant to higher concentrations of 5FT, which was derived from strain 251 and produced L-tryptophan, the synthesis of all the trypto-phan enzymes except PRT had been derepressed. In mutants resistant to high concentrations of 5FT, strains 1288 and 399, which were derived directly from the wild-type strain and produced L-tryptophan, the syntheses of all the tryptophan enzymes and of all except TS had been derepressed, respectively, in addition to desensitization of AS to feedback inhibition. From these results, it was concluded that the syntheses of the five enzymes in the tryptopha