Saccharomyces kluyveri mannoprotein mutants

Abstract

Saccharomyces kluyveri cells were mutagenized with ethylmethane sulfonate and, after the cells had grown a few divisions to express any altered cell-surface antigenic structure, the culture was treated with rabbit antiserum directed against the wild type cells in order to enrich for mutants that failed to precipitate with the serum. Several mutant clones were obtained that proved to be altered in the carbohydrate component of the cell-wall mannoprotein. Whereas the wild type strain produces mannoprotein with carbohydrate side chains up to 8 mannose units in length (Zhang, W.-J., and Ballou, C. E. (1981) J. Biol. Chem. 256, 10073-10079), one of the mutants (designated mnn1) has side chains no longer than 3 mannoses. From a comparison of the carbohydrate structures of the mutant and wild type mannoproteins by beta-elimination, acetolysis, and methylation, it appears that this mutant is unable to add mannose in alpha 1 leads to 3 linkage to the alpha 1 leads to 2-linked di- and trisaccharide side chains, thus preventing elongation and branching of the chains that occur in the wild type. Another mutant, designated mnn2, was unable to make the octasaccharide chain, whereas a third class made oligosaccharides of all sizes but did so in ratios that differed from the wild type. These three classes of mutants involve different loci because they complemented each other in the heterozygous diploids.