Multicopy suppressor analysis of thermosensitive YIP1 alleles implicates GOT1 in transport from the ER.

Yip1p belongs to a conserved family of membrane-spanning proteins that are involved in intracellular trafficking. Studies have shown that Yip1p forms a heteromeric integral membrane complex, is required for biogenesis of ER-derived COPII vesicles, and can interact with Rab GTPases. However, the role of the Yip1 complex in vesicle budding is not well understood. To gain further insight, we isolated multicopy suppressors of the thermosensitive yip1-2 allele. This screen identified GOT1, FYV8 and TSC3 as novel high-copy suppressors. The strongest suppressor, GOT1, also displayed moderate suppressor activity toward temperature-sensitive mutations in the SEC23 and SEC31 genes, which encode subunits of the COPII coat. Further characterization of Got1p revealed that this protein was efficiently packaged into COPII vesicles and cycled rapidly between the ER and Golgi compartments. Based on the findings we propose that Got1p has an unexpected role in vesicle formation from the ER by influencing membrane properties.