PORPHYRIN BIOSYNTHESIS IN NORMAL AND HEME MUTANTS OF SACCHAROMYCES-CEREVISIAE - STUDIES ON THE INHERITANCE OF THE HEM R+ PHENOTYPE

Heme biosynthesis was studied in the segregants of Saccharomyces cerev isiae (DW10 tetrade 2) from D27 and D27/C6 mating, as a function of th e carbon source in the growth medium and the physiological state of th e cells. The effects of the HEM Rf gene on the 5-aminolevulinate synth ase (ALA-S) and 5-aminolevulinate dehydratase (ALA-D) activities of he me biosynthesis in cells grown on nonfermentable and fermentable carbo n sources were compared. Profiles obtained for both strains grown on a fermentable carbon source (glucose) were identical. However, in the p resence of a nonfermentable carbon source (ethanol), they behave quite different, as if the mutation could only be expressed under these gro wth conditions. Moreover, their behavior is similar to that found for the parental strains, indicating that for the mutant its particular be havior might be inheritedly linked to the HEM R+ gene, which in turn a ffects some regulatory aspects of ALA synthesis explaining its charact eristic phenotype.