THE ESSENTIAL SCHIZOSACCHAROMYCES-POMBE GPI1(-YEAST GPI ANCHORING MUTANT AND IS REQUIRED FOR EFFICIENT CELL-SEPARATION() GENE COMPLEMENTS ABAKERS)

The Schizosaccharomyces pombe gpi(+) gene was cloned by complementatio n of the Saccharomyces cerevisiae gpil mutant, which has temperature-s ensitive defects in growth and glycosyl phosphatidylinositol (GPI) mem brane anchoring of protein, and which is defective in vitro in the fir st step in GPI anchor assembly, the formation of n-acetylglucosaminyl phosphatidylinositol (GlcNAc-PI). S. pombe gpil(+) encodes a protein w ith 29% identity to amino acids 87-609 of the S. cerevisiae protein, a nd is the functional homolog of the S. cerevisiae Gpil protein, for it restores [H-3]inositol-labelling of protein and in vitro GlcNAc-PI sy nthetic activity to both S. cerevisiae gpil and gpil::URA3 cells. Disr uption of gpil(+) is lethal. Haploid Delta gpil(+)::his7(+) spores ger minate, but proceed through no more than three rounds of cell division , many cells ceasing growth as binucleate, septate cells with thickene d septa. These results indicate that GPI synthesis is an essential fun ction in fission yeast, and suggest that GPI anchoring is also require d for completion of cytokinesis. The nucleotide sequence reported will appear in the GenBank Nucleotide Sequence database under the Accessio n Number U77355.