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 vesicles with the plasma membrane in yeast. Mutation of a methionine-based sorting signal in the cytoplasmic domain of either Sncp inhibits Sncp endocytosis and prevents recycling of Sncp to the Golgi after exocytosis. snc1-M43A 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 also partially suppresses the growth and secretion phenotypes of a snc deletion, we propose that enhanced degradation of dihydrosphingosine-1-phosphate allows an alternative protein to replace Sncp as the secretory vesicle v-SNARE.