Genetic Changes in Regulation Occurring in the Tryptophan Biosynthetic Pathway of l-Tryptophan Producing Mutants Derived from Bacillus subtilis K

The regulatory mechanism for l-tryptophan (l-Trp) synthesis was compared between the wild type strain and l-Trp producing mutants of B. subtilis K. In the wild type strain, indolmycin (IM) repressed the synthesis of anthranilate synthetase (AS) more strongly than 5-fluorotryptophan ? (5FT), which repressed AS to the same extent as l-Trp did. 5FT inhibited the activity of AS as strongly as l-Trp did, while IM had no inhibitory effect. In the 5FT resistant strains, the syntheses of AS and tryptophan synthetase (TS-B) were markedly increased by genetic derepression, while AS remained still sensitive to the feedback inhibition by l-Trp. The facts that IM repressed the syntheses of AS and TS-B in the strain which was 5FT^r and IM^S, and did not repress those in the IM-resistant mutant suggested that IM acts as a co-repressor in a different way from 5FT.