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. PSMC5 belongs to the heterohexameric ring of AAA (ATPases associated with diverse cellular activities) proteins that unfolds ubiquitinated target proteins that are concurrently translocated into a proteolytic chamber and degraded into peptides. Component of the 19S proteasome regulatory particle complex. The 26S proteasome consists of a 20S core particle (CP) and two 19S regulatory subunits (RP) (By similarity). The regulatory particle is made of a lid composed of 9 subunits, a base containing 6 ATPases including PSMC5 and few additional components (By similarity). Component of a complex with USP49 and RUVBL1 (By similarity). Interacts with PRPF19 (PubMed:17349974). Interacts with TRIM5 (By similarity). Interacts with NDC80 (By similarity). Interacts with PAAF1 (By similarity). Interacts, in vitro, with the thyroid hormone receptor (in a thyroid hormone T3-dependent manner) and with retinoid X receptor (RXR) (PubMed:8598193). Interacts with ERCC6 (By similarity). Belongs to the AAA ATPase family.