Biosynthetic pathway and physiological role of pyruvylated galactose-containing oligosaccharides in fission yeast.

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In the fission yeast Schizosaccharomyces pombe, galactose residues are transferred to N- and O-linked oligosaccharides of glycoproteins by galactosyltransferases in the lumen of the Golgi apparatus. Cell surface glycoproteins play a key role in flocculation and filamentous invasive growth in yeasts. We identified fission yeast gsf2+, encoding a flocculin that binds to galactose residues located on cell surface glycoconjugates. Flocculation and invasive growth of S. pombe is tightly controlled by gsf2+ expression. MADS-box transcription factor Mbx2 regulates nonsexual flocculation by inducing gsf2+ expression. S. pombe appears to have a unique galactose-specific recognition system in which Gsf2p/flocculin plays an essential role in mediating cell-cell interactions. Furthermore, we characterized a putative S. pombe pyruvyltransferase, Pvg1p, and the recombinant Pvg1p transferred pyruvyl residues from phosphoenolpyruvate specifically to beta-linked galactose.