Molecular characterization of the SEC1 gene of Saccharomyces cerevisiae: subcellular distribution of a protein required for yeast protein secretion.

Strains of Saccharomyces cerevisiae harbouring temperature-sensitive mutations in the SEC1 and SEC5 genes exhibit an accumulation of post-Golgi secretory vesicles at 37 degrees C. We have cloned a fragment of yeast DNA which carries two distinct genes, one of which complements a sec1 mutation, and the other a sec5 mutation. Genetic test confirm that the sec1-complementing gene is indeed SEC1, and is essential for cell growth. Nucleotide sequence analysis reveals that the cloned SEC1 gene is the same as a previously sequenced sec1-complementing gene. The SEC1 sequence encodes a protein of 724 amino acids with a predicted molecular mass of 83 kDa. Antibodies purified from a polyclonal antiserum raised against the protein product of the cloned gene recognize a yeast protein of apparent molecular mass 78 kDa which is found in a detergent-resistant association with a rapidly sedimenting yeast subcellular fraction, behaviour which is suggestive of an interaction with a component of the yeast cytoskeleton.