Porphyrin biosynthesis in normal and haem mutants of Saccharomyces cerevisiae. Studies on the inheritance of the HEM R+ phenotype.

Heme biosynthesis was studied in the segregants of Saccharomyces cerevisiae (DW10 tetrade 2) from D27 and D27/C6 mating, as a function of the carbon source in the growth medium and the physiological state of the cells. The effects of the HEM R+ gene on the 5-aminolevulinate synthase (ALA-S) and 5-aminolevulinate dehydratase (ALA-D) activities of heme biosynthesis in cells grown on nonfermentable and fermentable carbon sources were compared. Profiles obtained for both strains grown on a fermentable carbon source (glucose) were identical. However, in the presence of a nonfermentable carbon source (ethanol), they behave quite different, as if the mutation could only be expressed under these growth conditions. Moreover, their behavior is similar to that found for the parental strains, indicating that for the mutant its particular behavior might be inheritedly linked to the HEM R+ gene, which in turn affects some regulatory aspects of ALA synthesis explaining its characteristic phenotype.