Multiple functions of ergosterol in the fission yeast Schizosaccharomyces pombe

1 Department of Life Sciences, Faculty of Agriculture, Kagawa University, Miki-cho, Kagawa 761-0795, Japan 2 Research Center, Asahi Glass Co. Ltd, Yokohama, Kanagawa 221-8755, Japan 3 National Research Institute of Brewing, 3-7-1 Kagamiyama, Higashi Hiroshima, Hiroshima 739-0046, Japan 4 Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi Hiroshima, Hiroshima 739-8526, Japan Correspondence Kaoru Takegawa takegawa{at}ag.kagawa-u.ac.jp Sterols are a major class of membrane lipids in eukaryotes. In Schizosaccharomyces pombe , sterol 24-C-methyltransferase (Erg6p), C-8 sterol isomerase (Erg2p), C-5 sterol desaturase (Erg31p, Erg32p), C-22 sterol desaturase (Erg5p) and C-24 (28) sterol reductase (Sts1p/Erg4p) have been predicted, but not yet determined, to catalyse a sequence of reactions from zymosterol to ergosterol. Disruption mutants of these genes were unable to synthesize ergosterol, and most were tolerant to the polyene drugs amphotericin B and nystatin. Disruption of erg31 + or erg32 + did not cause ergosterol deficiency or tolerance to polyene drugs, indicating that the two C-5 sterol desaturases have overlapping functions. GFP-tagged DRM (detergent-resistant membrane)-associated protein Pma1p localized to the plasma membrane in erg mutants. DRM fractionation revealed that the association between Pma1-GFP and DRM was weakened in erg6 but not in other erg mutants. Several GFP-tagged plasma membrane proteins were tested, and an amino acid permease homologue, SPBC359.03c, was found to mislocalize to intracellular punctate structures in the erg mutants. These results indicate that these proteins are responsible for ergosterol biosynthesis in fission yeast, similar to the situation in Saccharomyces cerevisiae . Furthermore, in fission yeast, ergosterol is important for plasma membrane structure and function and for localization of plasma membrane proteins. Abbreviations: CHX, cycloheximide; CPY, carboxypeptidase Y; DRM, detergent-resistant membrane; GFP, green fluorescent protein; LY, Lucifer Yellow CH; TX-100, Triton X-100 Three supplementary figures are available with the online version of this paper.