SEC62

Abstract sec62 mutants were originally identified in a selection for conditional lethal mutants that fail to localize a signal peptide-containing His4 chimera to the ER lumen1. Various derivations of this selection scheme have yielded mutant alleles of three other genes: sec611(see p. 31), sec632(see p. 34), and sec653(see p. 28). sec62 mutants accumulate untranslocated precursor forms of several secretory pathway polypeptides, including alpha factor and carboxypeptidase Y. The translocation of some proteins, including invertase, is only weakly affected by the sec62 mutation, whereas others, including dipeptidylaminopeptidase B, are not affected at aII. Whereas sec62 cells are temperaturesensitive for growth, they exhibit severe defects in protein translocation even at the “permissive” temperature of 24°C. Growth at lower temperatures (17°(), however, restores translocation to nearly wild type levels2. Deletion of SEC62 is lethaI4, indicating that it is an essential gene.