proteasome complex 26S proteasome cellular_component GO:0000502 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. proteasome intracellular protein-containing complex endopeptidase complex