THE 20S PROTEASOME MEDIATES THE DEGRADATION OF MOUSE AND YEAST ORNITHINE DECARBOXYLASE IN YEAST-CELLS

Ornithine decarboxylase (ODC), a key enzyme in the biosynthesis of pol yamines, is one of the most rapidly degraded proteins in mammalian cel ls. Recently it has been demonstrated that mammalian ODC is degraded i n vitro by the 26S protease that contains the 20S proteasome as its ca talytic core, in a reaction that does not require ubiquitin. Here, we show that yeast and mouse ODC are both rapidly degraded in yeast cells and that their degradation severely inhibited in a mutant yeast cell line defective in the chymotryptic activity of proteinase yscE, the ye ast 20S proteasome. These results provide compelling genetic support t o previous biochemical studies suggesting the involvement of the 20S p roteasome in the degradation of ornithine decarboxylase.