Gene-enzyme relations affecting tryptophan biosynthesis in Streptomyces coelicolor A3(2)

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Virginia Polytechnic Institute and State University

Earlier investigations indicated that the genes involved in the biosynthesis of tryptophan from anthranilic acid were located in at least two separate regions on the chromosome of Streptomyces coelicolor A3(2). Tryptophan-requiring mutants capable of utilizing indole mapped counterclockwise of hisC9 between hisC9 and proAl. Trp mutants unable to use indole in place of tryptophan mapped clockwise of hisC9 between hisC9 and ammA5.

Other genetic markers, located between proAl and hisC9, include leuAl, rif'B37 and thiC2. Twenty indole-utilizing Trp mutants were mapped relative to leuAl, rifB37 and thiC2. All but two recently isolated mutants, Trp-e8 and e22, mapped between rifB37 and thiC2. Genetic and enzymatic analyses of Trp-e8 and e22 indicate that these mutants map between hisC9 and ammA5, fail to complement each other in vivo and lack indoleglycerol phosphate synthase. Two mutants, Trp-e14 and 8, mapping between hisC9 and ammA5 were assayed for their tryptophan enzymes. Trp-el4 lacks tryptophan synthase B activity. Tryptophan synthase A activity was missing and tryptophan synthase B activity was relatively weak in crude extracts of Trp-8.

Anthranilate-PRPP phosphoribosyltransferase activity was not detected in crude extracts of two mutants, Trp-e6 and e10, mapping between rifB37 and thiC2.