proteasome complex 26S proteasome A large multisubunit complex which catalyzes protein degradation, found in eukaryotes, archaea and some bacteria. In eukaryotes, this complex consists of the barrel shaped proteasome core complex and one or two associated proteins or complexes that act in regulating entry into or exit from the core. GO:0000502 cellular_component go.owl pro.owl proteasome protein complex intracellular part endopeptidase complex