Component of the 26S proteasome, a multiprotein complex involved in the ATP-dependent degradation of ubiquitinated proteins. This complex plays a key role in the maintenance of protein homeostasis by removing misfolded or damaged proteins, which could impair cellular functions, and by removing proteins whose functions are no longer required. Therefore, the proteasome participates in numerous cellular processes, including cell cycle progression, apoptosis, or DNA damage repair. Within the complex, functions as a proteasomal ubiquitin receptor. Engages and activates 19S-associated deubiquitinases UCHL5 and PSMD14 during protein degradation. UCHL5 reversibly associate with the 19S regulatory particle whereas PSMD14 is an intrinsic subunit of the proteasome lid subcomplex. Component of the 19S proteasome regulatory particle complex. The 26S proteasome consists of a 20S core particle (CP) and two 19S regulatory subunits (RP). Interacts with the proteasomal scaffolding protein PSMD1. Interacts with deubiquitinase UCHL5; this interaction activates the auto-inhibited UCHL5 by deoligomerizing it. Interacts with UBQLN2 and ubiquitin. The Pru (pleckstrin-like receptor for ubiquitin) domain mediates interactions with PSMD1 and ubiquitin. Preferential binding to the proximal subunit of 'Lys-48'-linked diubiquitin allows UCHL5 access to the distal subunit. Ubiquitinated by UBE3C in response to proteotoxic stress. Belongs to the ADRM1 family.