A snc1 endocytosis mutant: Phenotypic analysis and suppression by overproduction of dihydrosphingosine phosphate lyase

The V-SNARE proteins Snc1p and Snc2p are required for fusion of secretory v esicles with the plasma membrane in yeast. Mutation of a methionine-based s orting signal in the cytoplasmic domain of either Sncp inhibits Sncp endocy tosis and prevents recycling of Sncp to the Golgi after exocytosis. snc1-M4 3A mutant yeast have reduced growth and secretion rates and accumulate post -Golgi secretory vesicles and fragmented vacuoles. However, cells continue to grow and secrete for several hours after de novo Snc2-M42A synthesis is repressed. DPL1, the structural gene for dihydrosphingosine phosphate lyase , was selected as a high copy number snc1-M43A suppressor. Because DPL1 als o partially suppresses the growth and secretion phenotypes of a snc deletio n, we propose that enhanced degradation of dihydrosphingosine-1-phosphate a llows an alternative protein to replace Sncp as the secretory vesicle v-SNA RE.