BIOSYNTHESIS AND FUNCTION OF YEAST VACUOLAR PROTEASES - REVIEW

The yeast vacuole, which is equivalent to the lysosome of higher eukar yotes, is one of the best characterized degradative organelles. This r eview describes the biosynthesis and function of yeast vacuolar protea ses. Most of these enzymes are delivered to the vacuole via the early compartments of the secretory pathway and the endosome, while one of t hem is directly imported from the cytoplasm. The proteases are synthes ized as precursors which undergo many post-translational modifications before the final active form is generated. Proteolytic activation by removal of propeptides is performed by proteinase A and/or proteinase B in an intricate cascade-like fashion. Recent developments in the ana lysis of the functions of vacuolar proteolysis are described. Substrat es of the vacuolar proteases are mostly imported via endocytosis or au tophagocytosis, and vacuolar proteolysis appears to be mainly importan t under nutritional stress conditions and sporulation.