Characterization of tryptophan-requiring auxotrophs of Streptomyces venezuelae ISP5230

Abstract

The growth supplement requirements in minimal medium, the identity of metabolic intermediates accumulated, and the activity of tryptophan biosynfhetic enzymes detectable in cell extracts allowed the trp mutations in 10 auxotrophic strains of Streptomyces venezuelae ISP5230 to be determined. Three strains contained lesions in the trpA and two in the trpB subunits of tryptophan synthetase; two other strains were either double (trpA, trpB) mutants or contained a polar mutation in one of the subunit genes. Two strains with trpC mutations and one with a trpD mutation were also identified. When considered with information about the relative location of the auxotrophic markers obtained in this and earlier studies, the results indicated that trpA, trpB, and trpC are clustered near hisA and hisB, while trpD is in a separate position near nicB. The arrangement resembles that of the comparable genes in Streptomyces coelicolor A3(2). Key words: tryptophan auxotrophs, Streptomyces venezuelae, mutation loci, tryptophan biosynthesis genes.