Lysosomal and non-lysosomal proteolysis in the eukaryotic cell: studies on yeast.

Introduction Proteolysis is an essential tool in regulating cellular functions at the post-translational level. The yeast Saccharomyces cereviszize serves as an excellent model organism for studying the biological role of proteolysis in the eukaryotic cell as it is accessible to the combination of biochemical, genetic and molecular biological techniques [ 1-31. As found for mammalian cells, two major proteolytic systems involved in the degradation of proteins have been found in yeast up to now: a lysosomal (vacuolar) system and a cytoplasmic system [4, 51. The lysosoma1 system is composed of two endopeptidases and five exopeptidases [3-51. The cytoplasmic system involved in protein degradation, elucidated so far, consists of proteinase yscE, the equivalent of the mammalian proteasome/multicatalytic-multifunctional proteinase [6, 71. Here we report on the function of both the lysosomal and the cytoplasmic proteolytic system in cellular life.