Processing pathway for protease B of Saccharomyces cerevisiae

The vacuolar protease B of Saccharomyces cerevisiae is a subtilisin-like protease encoded by the PRB1 gene. Antibodies raised against a synthetic peptide and an Escherichia coli-derived PRB1 open reading frame (ORF) protein cross-react with authentic protease B from yeast. By using these antibodies, the posttranslational biosynthetic pathway of protease B has been elucidated. Preproprotease B is a 76-kD unglycosylated precursor that enters the endoplasmic reticulum (ER), where it receives one asparagine-linked (Asn-linked) and an undetermined number of non-Asn-linked carbohydrate side chains. The large glycosylated intermediate is proteolytically processed to a 39-kD form before exiting the ER. In the Golgi complex, the 39-kD form becomes 40 kD, due to elaboration of the Asn-linked side chain. The carboxyterminal end of the 40-kD proprotease B undergoes protease A-mediated processing to a 37-kD intermediate, which in turn is quickly processed to 31-kD mature protease B. The ultimate processing step removes a peptide containing the Asn-linked chain; mature PrB has only non-Asn-linked carbohydrate.