Processing and secretion of the alkaline extracellular protease (AEP) from the yeast Yarrowia lipolytica was studied by pulse-chase and immunoprecipitation experiments. Over half of newly synthesized AEP was secreted by 6 min. Over 99% of AEP activity which was external to the cytoplasmic membrane was located in the supernatant medium. Polypeptides of 55, 52, 44, 36, and kifodaltons derived from the proregion of AEP indicated that one major processing pathway was 55K-*52K-*32K. The gene coding for AEP (XPR2) was cloned and sequenced. The sequence and the immunoprecipitation results suggest that AEP is originally synthesized with an additional preprol-proII-proIlI amino-terminal region. Processing definitely involves cleavage(s) after pairs of basic amino acids and the addition of one N-linked oligosaccharide. Signal peptidase cleavage, dipeptidyl aminopeptidase cleavages, and at least one additional proteolytic cleavage may also be involved.

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