Genetic Control of Yeast Mannan Structure

Abstract

Abstract Analysis of Saccharomyces cerevisiae X2180 phosphomannan, with a mannose to phosphate ratio of 38, has shown that it contains phosphorylated side chains with the structure [see PDF for equation] This unit apparently arises in the mannan by the addition of α(1→3)-linked mannose units to existing mannosylphosphorylmannotriose side chains from the action of an α(1→3)mannosyltransferase. It is postulated that the immunochemical difference between S. cerevisiae X2180 and strain 4484-24D (Antalis, C., Fogel, S., and Ballou, C. E. (1973) J. Biol. Chem. 248, 4655–4659) results from the presence or absence of this single enzyme. In its absence, the mannosylphosphate groups that are added to mannotriose side chains through the action of a mannosylphosphate transferase act as characteristic antigenic determinants in the 4484-24D mannan. However, in strain X2180, or in the hybrid diploid obtained by a cross of X2180 with 4484-24D, these mannosylphosphate groups are converted to α(1→3)-mannobiosylphosphate groups. In the resulting mannan, the various terminal α(1→3)-linked mannobiose units confer on the molecule a new immunological specificity.