The 26S proteasome degrades polyubiquitinated proteins in the cytoplasm and nucleus. It is formed from a cylindrical catalytic core 20S proteasome capped at each end by a regulatory 19S particle. The 19S regulatory particle recognizes, unfolds, and translocates ubiquitinated proteins into the catalytic core particle in an ATP-dependent manner. 'Rpn' subunits are non-ATPase subunits located in the base and lid subcomplexes of the regulatory particle (Adapted from FBrf0215459 and PMID:28583440.)