Targeting of aminopeptidase I to the yeast vacuole ts mediated by Ssa1p, acytosolic member of the 70-kDa stress protein family

The two cytosolic members of the highly conserved 70-kDa stress protein fam ily, Ssa1p and Ssa2p, were specifically retained by the prepro-NH2 extensio n of the vacuolar aminopeptidase I precursor (pAPI) conjugated to agarose ( Sulfolink). A temperature-sensitive mutant strain a1(ts)a234 (ssa1(ts) ssa2 ssa3 ssa4), when incubated at the restrictive temperature, was able to ass emble the API precursor into dodecamers, but failed to pack pAPI into vesic les and to convert it into mature API (mAPI), a process that occurs in the vacuole. Altogether these results indicate that Ssa1p mediates the targetin g of pAPI to the vacuole.