Biosynthetic Pathway and Physiological Role of Galactose-Containing Oligosaccharides in Fission Yeast Schizosaccharomyces pombe

In recent years, the fission yeast Schizosaccharomyces pombe has attracted interest as a promising unicellular eukaryote model for studies on the biosynthetic pathway and oligosaccharide structures of glycoproteins. The glycoproteins of S. pombe contain a large amount of galactose in addition to mannose, indicating that S. pombe is equipped with mechanisms for galactosylation of glycoprotein, like mammalian cells. To elucidate the physiological role of galactosylation, we isolated an S. pombe mutant (gmsl) defective in protein galactosylation. We found that disruption of the ginsl⁺ gene (Δgmsl) in S. pombe led to a complete loss of cell surface galactosylation, due to a defect in the transport of UDP-galactose as substrate for galactosyltransferase from cytosol into the lumen of the Golgi apparatus. Therefore, the Δgmsl strain is very useful for the analysis of the phenotypes of S. pombe cells lacking galactose residues and for the elucidation of the galactosylation mechanism. Although galactose residues are not essential for growth of S. pombe cells, the galactosylation of protein is required for the maintenance of normal cell shape, sexual agglutination, tolerance toward various drugs, and non-sexual flocculation in S. pombe.