Protease that specifically cleaves 'Lys-48'-linked polyubiquitin chains. Deubiquitinating enzyme associated with the 19S regulatory subunit of the 26S proteasome. Putative regulatory component of the INO80 complex; however is inactive in the INO80 complex and is activated by a transient interaction of the INO80 complex with the proteasome via ADRM1. Thiol-dependent hydrolysis of ester, thioester, amide, peptide and isopeptide bonds formed by the C-terminal Gly of ubiquitin (a 76-residue protein attached to proteins as an intracellular targeting signal). Activated by ADRM1. Inhibited by interaction with NFRKB. Component of the 19S (PA700) regulatory complex of the 26S proteasome. Interacts with ADRM1 and NFRKB; in vitro ADRM1 and NFRKB compete for interaction with UCHL5. Component of the INO80 complex; specifically part of a complex module associated with N-terminus of INO80. Associates with the proteasome 19S subunit in the cytoplasm. Associates with the INO80 complex in the nucleus. Experimental confirmation may be lacking for some isoforms. Belongs to the peptidase C12 family.