Intracellular transport of GPI-anchored proteins by yeast.

We have investigated the effects of an inhibitor of ceramide biosynthesis on the glycosylphosphatidylinositol (GPI)-anchoring and intracellular transport of the yeast Gas1 protein. No effect on anchor attachment was demonstrable, but a selective delay in transport from the endoplasmic reticulum to the Golgi complex was observed. The compound also blocked remodeling of GPI-anchors from their base-sensitive to base-resistant forms. A recessive mutation was found that caused resistance to the drug, restored transport of Gas1p, but did not restore ceramide biosynthesis in the presence of the inhibitor. Our results suggest that intracellular transport of GPI-anchored proteins is stimulated by new ceramide synthesis. The role of ceramide may be direct or may be through its use in the remodeling of GPI-anchored proteins other than Gas1p. The need for ceramide can be overcome in the mutant strain.