SCHIZOSACCHAROMYCES-POMBE MUTANTS THAT ARE DEFECTIVE IN GLYCOPROTEIN GALACTOSYLATION

Several mutants of Schizosaccharomyces pombe were obtained that are de fective in protein glycosylation. One of the mutants, strain Sp550, ma kes galactomannoproteins with about half of the wild-type amount of ga lactose, whereas another strain, Sp137, makes glycoproteins that are a lmost devoid of galactose. Nondenaturing gel electrophoresis of cell e xtracts of both mutants revealed that they make invertases with a grea tly increased mobility relative to the wild type. Additional study sho wed that Sp137 invertase has a subunit molecular mass that is about ha lf that reported for the wild-type enzyme, owing to a reduction in car bohydrate content, whereas the native multimeric state appears unalter ed. Structural studies on bulk cell-wall glycoprotein from Sp137 showe d that the N-Linked carbohydrate chains consist of a typical branched core oligosaccharide to which is attached an unsubstituted alpha 1-->6 -polymannose outer chain. Consequently, the cells are agglutinated by antibodies against alpha 1-->6-linked mannose and have N-linked carboh ydrate chains that are structurally analogous to the mnn2 mutant of Sa ccharomyces cerevisiae.