Characterization of a Schizosaccharomyces pombe mutant deficient in UDP-galactose transport activity

In fission yeast, Schizosaccharomyces pombe, the carbohydrate components of the cell wall consist of galactomannan, unlike in Saccharomyces cerevisiae. We previously found that the disruption of gms1⁺, a gene encoding the UDP-galactose transporter required for the synthesis of galactomannan, led to the complete defect of cell surface galactosylation in Sz. pombe. The Δgms1 strain is therefore useful for the analysis of physiological properties of galactose residues in Sz. pombe. The deletion strain of gms1⁺ was viable; however, it showed an aberrant cell morphology and increased sensitivities to digestion with β-glucanase and to various drugs, such as hygromycin B, sodium orthovanadate and Calcofluor white. A reduction of galactomannan layers of the cell wall in the Δgms1 strain was observed by scanning and transmission electron microscopic analyses. The addition of osmotic stabilizer suppressed the morphologic defect of the Δgms1 cells, while other phenotypes were weakly suppressed. The Δgms1 (h⁹⁰) strain was incapable of sexual conjugation during nutritional starvation. These results suggest that the cell surface galactosylation is required not only for non-sexual flocculation but also for sexual conjugation in Sz. pombe.