In vivo processing of nonanchored yapsin 1 (Yap3p)

A C-terminally truncated form of yapsin 1 (yeast aspartic protease 3) was o verexpressed in yeast and its processing through the secretory pathway was followed by pulse-labeling and immunoprecipitation studies. In the soluble cell extract, three forms of yapsin 1-87, 74, and 18 kDa-were found. Identi fication of these forms of yapsin 1 using different antisera suggests that the 87-kDa form is pro-yapsin 1, which is processed into two subunits, alph a (18 kDa) and beta (74 kDa), by cleavage at a loop region not found in tra ditional aspartic proteases. By use of a temperature-sensitive mutant strai n, sec18, the generation of the two subunits was found to occur in the endo plasmic reticulum. An active site-mutated yapsin 1 was not processed into t he two subunits, suggesting that this process occurs in an autocatalytic ma nner. (C) 2000 Academic Press.