Proteins in all cells turnover continuously such that rigorous control of proteolysis is required
to govern levels of proteins with vastly different half-lives and actions including those
regulating transcription, metabolic pathways, or the breakdown of muscle proteins to amino
acids used in gluconeogenesis or the synthesis of new proteins. Critical cellular functions
would be disrupted without precise regulation of protein degradation. Thus, it is surprising
that the bulk of protein in all cells is degraded by the ATP-dependent, ubiquitin-proteasome …