Genetic control of yeast mannan structure: mapping genes mnn2 and mnn4 in Saccharomyces cerevisiae

Two mutations concerned with mannan biosynthesis in the yeast Saccharomyces cerevisiae have been mapping. The mnn2 mutation, which affects the addition to the polysaccharide backbone of the first side-chain D-mannose unit in alpha1-leads to2 linkage, was located on chromosome II linked to the centromere and the gall locus. The mn4 locus, which regulates the synthesis of mannosylphosphate groups on the mannan side chains, was placed on chromosome XI near trp3 and ural and a locus previously reported to regulate the ability of a S. diastaticus strain to bind alcian blue (Friis and Ottolenghi, 1970). The mnn4 mutant also fails to bind alcain blue, but the gene responsible for alcian blud binding in this strain segregates independently from the dye-binding locus of S. diastaticus, and therefore must be a different gene. A diploid heterozygous for mnn4 fails to bind dye, indicating dominance of this mutant genotype. The alcian blue dye binding locus dbll, reported to Friis and Ottolenghi (1970), is also dominant. Thus, there are at least two independent genes that control the formation of the mannosylphosphate units in the mannan side chains, and both have the property of dominance in the mutant form.