ISOLATION, CHARACTERIZATION AND MAPPING OF PYRIMIDINE AUXOTROPHS OF PHYCOMYCES-BLAKESLEEANUS

A total of seven pyrimidine auxotrophs of Phycomyces were isolated fro m among 5-fluoroorotate acid (5-FOA)-resistant mutants. They were clas sified by complementation into two groups. A representative mutant str ain belonging to one group was deficient in orotate phosphoribosyl tra nsferase (OPRTase; EC 2.4.2.10) activity; the mutant strain belonging to the second group was deficient in orotidine-5'-monophosphate decarb oxylase (OMPdecase; EC 4.1.1.23). These mutants are defective in the g enes pyrF and pyrG respectively. The results from random spore analysi s, tetrad analysis, and gene-centromere distances showed that these tw o markers are located in linkage group VI, with pyrG being a proximal marker and pyrF a distal one.