Mutagenesis of Schizosaccharomyces pombe cells yielded a strain that made reduced amounts of invertase. A comparison of the O- and N-linked carbohydrate chains of the wild-type and mutant glycoproteins revealed that a single type of alpha 1-->2-linked mannose was missing in the mutant. Analysis of the wild-type galactomannoprotein showed that it contained a heterogeneous small "core" oligosaccharide fraction linked to asparagine with sugar compositions that ranged from Man9(GlcNAc)2- to Gal4Man10(GlcNAc)2-. The galactose units are in terminal positions of a Man10(GlcNAc)2- unit that is similar to the mannoprotein core of Saccharomyces cerevisiae. Attached to this core in a larger oligosaccharide fraction is an alpha 1-->6-linked polymannose chain that is substituted at position 2 with alpha-linked mannose and galactose. The O-linked sugars consist of mannose, alpha 1-->2-linked mannosylmannose and alpha 1-->2-linked galactosylmannose, along with small amounts of tri- and tetrasaccharides. The glycosylation mutant lacks alpha 1-->2-linked mannose on both the O-linked chains and the outer chain of the large N-linked chains, suggesting that it may be defective in regulation of an alpha 1,2-mannosyltransferase that adds mannose to glycoproteins in the Golgi.