REPRESSION AND INHIBITION OF INDOLE-SYNTHESIZING ACTIVITY IN NEUROSPORA CRASSA

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Abstract
Lester, Gabriel (Worcester Foundation for Experimental Biology, Shrewsbury, Mass.). Repression and inhibition of indole-synthesizing activity in Neurospora crassa . J. Bacteriol. 82: 215–223. 1961.—The possibility of repression and feedback inhibition as regulating mechanisms for the synthesis of tryptophan by Neurospora crassa has been examined in a tryptophan auxotroph which accumulates indole (and indole-glycerol). Indole-synthesizing activity was determined with germinated conidia suspended in medium lacking tryptophan. This activity was almost absent from cells cultured on germination medium containing more than 1.0 μmole l -tryptophan per ml, and increased with decreasing concentrations of l -tryptophan. A similar depression of the formation of indole synthesizing activity was caused by 6-methyl- and d -tryptophan, and less effectively by 5-methyltryptophan; 4-methyltryptophan was slightly stimulatory. Preformed indole synthesizing activity was inhibited by l -tryptophan, 4- and 6-methyltryptophan, and to a lesser extent by 5-methyltryptophan; d -tryptophan had no effect in this respect. The inhibition of preformed activity was partially reversed by anthranilic acid, which is a precursor of indole. However, anthranilic acid did not increase indole synthesis by cells wherein the formation of indole-synthesizing activity had been depressed by culture in the presence of high concentrations of l - or d -tryptophan. These observations indicate that regulation of tryptophan synthesis in N. crassa might result from the action of tryptophan as a repressor and as a feedback inhibitor. The relation of these results to other regulatory systems is discussed.