Our laboratory has worked on many aspects of the biochemistry and physiology of intracellular protein degradation. Our current work involves a number of inter-related projects focusing on aspects of proteasome biochemistry and physiology. The following projects are in progress: We are determining the molecular and cellular mechanisms by which the 26S proteasome is assembled from 20S proteasome and PA700 subcomplexes. As part of this project we also are using high-throughput screening to identify chemicals that modulate this process. We will use such chemicals as novel investigational tools to discover additional mechanistic and regulatory features of 26S proteasome assembly and as candidates for new proteasome-based drugs. We are determining the mechanisms by which cells establish the relative content and distribution of multiple proteasome holoenzymes, and the relative cellular functions of these different proteasome subtypes including those that are ubiquitin-independent. We are also determining how process of holoenzyme selection and distribution is regulated and altered under various physiologic and pathologic conditions. We are examining the possible physiologic role of 20S proteasomes in the absence of regulatory complexes. This topic has important implications for the degradation of proteins with abnormal structures such as occur in various neurodegenerative diseases. We are determining the molecular and cellular roles of PI31, the most poorly understood proteasome regulatory protein. We are examining how PI31 selectively regulates proteasome function under highly specialized physiologic conditions.