STRUCTURAL AND FUNCTIONAL-CHARACTERIZATION OF SEC66P - A NEW SUBUNIT OF THE POLYPEPTIDE TRANSLOCATION APPARATUS IN THE YEAST ENDOPLASMIC-RETICULUM

SEC66 encodes the 31.5-kDa glycoprotein of the Sec63p complex, an inte gral endoplasmic reticulum membrane protein complex required for trans location of presecretory proteins in Saccharomyces cerevisiae. DNA seq uence analysis of SEC66 predicts a 23-kDa protein with no obvious NH2- terminal signal sequence but with one domain of sufficient length and hydrophobicity to span a lipid bilayer. Antibodies directed against a recombinant form of Sec66p were used to confirm the membrane location of Sec66p and that Sec66p is a glycoprotein of 31.5 kDa. A null mutati on in SEC66 renders yeast cells temperature sensitive for growth. sec6 6 cells accumulate some secretory precursors at a permissive temperatu re and a variety of precursors at the restrictive temperature. sec66 c ells show defects in Sec63p complex formation. Because sec66 cells aff ect the translocation of some, but not all secretory precursor polypep tides, the role of Sec66p may be to interact with the signal peptide o f presecretory proteins.