HIGH EXPRESSION OF THE YEAST SYNTAXIN-RELATED VAM3 PROTEIN SUPPRESSESTHE PROTEIN-TRANSPORT DEFECTS OF A PEP12 NULL MUTANT

The Pep12 protein of Saccharomyces cerevisiae is a member of the synta xin family thought to function as target membrane receptor (t-SNARE) f or vesicular intermediates travelling between the Golgi apparatus and the vacuole. Exploiting the temperature-sensitive growth phenotype of pep12 deletion strains, we identified VAM3 as a multicopy suppressor. Vam3p is another syntaxin-related protein which on high expression res tored vacuole acidification of pep12 null mutants and effectively supp ressed their sorting and maturation defects of vacuolar hydrolases. We conclude that Vam3p acts either as a bypass suppressor or by function ally replacing Pep12p at an endosomal, prevacuolar compartment. (C) 19 97 Federation of European Biochemical Societies.