The mechanism of interallelic complementation at the INO1 locus in yeast: immunological analysis of mutants.

The ino1 locus of yeast has been demonstrated to be the structural gene for the repressible enzyme, L-myo-inositol-1-phosphate synthase (Donahue and Henry 1981 a). We have screened a large number of allelic representatives of the ino1 locus for the presence of protein which cross reacts with antibody produced in response to purified wild type inositol-1-phosphate synthase. Approximately 50% of all ino1 representatives screened by immunoprecipitation produce a protein of 62,000 molecular weight, identical in size to the wild type enzyme subunit. These mutants (termed crm+) were tested for expression of the 62,000 MW protein under conditions which are repressing for the wild type enzyme (greater than 25 microM exogenous inositol). The protein produced by the crm+ mutants, like the active enzyme in wild type yeast, is repressed in the presence of high levels of exogenous inositol. In addition, we have reassessed the interallelic complementation pattern observed among mutants at the ino1 locus. The entire pattern of interallelic complementation is temperature sensitive.