Gpi1, a Saccharomyces cerevisiae protein that participates in the first step in glycosylphosphatidylinositol anchor synthesis

The temperature-sensitive Saccharomyces cerevisiae gpi1 mutant is blocked in [H-3]inositol incorporation into protein and defective in the synthesis of N-acetylglucosaminylphosphatidylinositol, the first step in glycosylphosphatidylinositol (GPI) anchor assembly (Leidich, S, D., Drapp, D, A, and Orlean, P, (1994) J, Biol, Chem. 269, 10193-10196). The GPI1 gene, which encodes a 609-amino acid membrane protein, was cloned by complementation of the temperature sensitivity of gpi1 and corrects the mutant's [H-3]inositol labeling and enzymatic defects, Disruption of GPI1 yields viable haploid cells that are temperature-sensitive for growth, for [H-3]inositol incorporation into protein, and for GPI anchor dependent processing of the Gas1/Ggp1 protein and that lack in vitro N-acetylglucosaminylphosphatidylinositol synthetic activity, The Gpi1 protein thus participates in GPI synthesis and is required for growth at 37 degrees C. When grown at a semipermissive temperature of 30 degrees C, gpi1 cells and gpi1::URA3 disruptants form large, round, multiply budded cells with a separation defect, Homozygous gpi1/gpi1, gpi1::URA3/gpi1::URA3, gpi2/gpi2, and gpi3/gpi3 diploids undergo meiosis, but are defective in ascospore wall maturation for they fail to give the fluorescence due to the dityrosine-containing layer in the ascospore wall, These findings indicate that GPIs have key roles in the morphogenesis and development of S, cerevisiae.