INOSITOL MUTANTS OF SACCHAROMYCES CEREVZSZAE: MAPPING THE inol LOCUS AND CHARACTERIZING ALLELES OFTHE inol, in02 AND in04 LOCI

An extensive genetic analysis of inositol auxotrophic mutants of yeast is reported. The analysis includes newly isolated mutants, as well as those pre- viously reported (CULBERTSON and HENRY 1975). Approximately 70% of all inositol auxotrophs isolated are shown to be alleles of the inol locus, the struc- tural gene for inositol-I-phosphate synthase, the major enzyme involved in inositol biosynthesis. Alleles of two other loci, in02 and ino4, comprise 9% of total mutants, with the remainder representing unique loci or complementa- tion groups. The inol locus was mapped by trisomic analysis with an n + l disomic strain constructed with complementing alleles at this locus. The inol locus is shown to be located between urn2 (11.1 CM) and cdc6 (21.8 CM) on chromosome X. An extended map of chromosome X of yeast is presented. Unlike most yeast loci, but similar to the his1 locus, the inol locus lacks allelic representatives that are suppressible by known suppressors. This finding sug- gests that premature termination of translation of the inol gene product may be incompatible with cell viability.