ABSTRACT
The proteasome is a large subcellular organelle present in all cells and is composed of a multisubunit protein complex that is the site for ATP-dependent degradation of ubiquitin-tagged proteins. The proteasome is responsible for the degradation of the majority of intracellular proteins in eukaryotic cells (1). The 26S proteasome is composed of a 20S proteolytic core flanked at each end by 19S regulatory complexes (Fig. 1). The 20S core consists of two alpha and two beta rings. Each beta ring consists of three active sites with trypsin, chymotrypsin, and postglutamylline hydrolytic activities. The amino terminus of the alpha subunits block access to the proteolytic chamber (2). The 26S proteasome is responsible for the degradation of the majority of regulatory proteins that control the cell cycle, transcription factor activation, apoptosis, and cell trafficking (3-5).
