SEC6 ENCODES AN 85 KDA SOLUBLE-PROTEIN REQUIRED FOR EXOCYTOSIS IN YEAST

The SEC6 gene encodes a protein required for an event leading to fusion of post-Golgi vesicles with the plasma membrane in Saccharomyces cerevisiae cells. The gene was cloned by complementation of the temperature-sensitive growth defect of a sec6-4 strain. The nucleotide sequence was determined and the longest open reading frame was found to encode an 85 kDa protein of 733 amino acids. The Sec6 protein is predicted to be hydrophilic and is found predominantly in the soluble fraction of a yeast lysate, in a species that sediments with a coefficient of 14S. No extensive homology was found with known proteins of the database. Gene disruption and marker rescue experiments indicate that SEC6 is a single copy gene essential for growth. Overproduction of Sec6p does not suppress any of the other late-acting sec mutants. yet sec6-4 does display synthetic lethality with sec8-9, suggesting that the two gene products may fulfill inter-related functions.