(-) MATING TYPE-SPECIFIC MUTANTS OF PHYCOMYCES DEFECTIVE IN SEX-PHEROMONE BIOSYNTHESIS

We have isolated the first mating type-specific mutants in mucoraceous fungi. Both mutants in Phycomyces blakesleeanus appear to be defectiv e in the same gene. The gene, present in both mating types, is necessa ry only in cultures of the (-) mating type. The gene codes for an enzy me in sex pheromone biosynthesis. The pheromone precursor made by the mutants is detectable only in cross-feeding experiments. The biologica l and solubility properties of the precursor suggest the precursor is 4-dihydrotrisporin, a metabolite of beta-carotene. Separate studies wi th beta-carotene-deficient mutants and Compound-P, a new chemically sy nthesized precursor of the pheromones, imply the constitutive level of enzymes for pheromone biosynthesis in Phycomyces is extremely low. In comparison, the level of enzymes for pheromone conversion to trispori c acid is higher. The mating type-specific mutants also catalyze the c onversion of (+) pheromone to trisporic acid. This finding was unexpec ted because literature models predicted this reaction was catalyzed by the same enzyme which catalyzed the conversion of 4-dihydrotrisporin to (-) pheromone-a reaction missing in the (-) mating type-specific mu tants. Thus, we propose a revised model for trisporic acid biosynthesi s. (C) 1996 Academic Press.