Proteasome inhibitors: valuable new tools for cell biologists.

Proteasomes are major sites for protein degradation in eukaryotic cells. The recent identification of selective proteasome inhibitors has allowed a definition of the roles of the ubiquitin-proteasome pathway in various cellular processes, such as antigen presentation and the degradation of regulatory or membrane proteins. This review describes the actions of these inhibitors, how they can be used to investigate cellular responses, the functions of the proteasome demonstrated by such studies and their potential applications in the future.