26S protease regulatory subunit 6B, also known as 26S proteasome AAA-ATPase subunit Rpt3, is an enzyme that in humans is encoded by the PSMC4 gene. This protein is one of the 19 essential subunits of a complete assembled 19S proteasome complex Six 26S proteasome AAA-ATPase subunits (Rpt1, Rpt2, Rpt3 (this protein), Rpt4, Rpt5, and Rpt6) together with four non-ATPase subunits (Rpn1, Rpn2, Rpn10, and Rpn13) form the base sub complex of 19S regulatory particle for proteasome complex. The gene PSMC4 encodes one of the ATPase subunits, a member of the triple-A family of ATPases which have a chaperone-like activity. This subunit has been shown to interact with an orphan member of the nuclear hormone receptor superfamily highly expressed in liver, and with gankyrin, a liver oncoprotein. Two transcript variants encoding different isoforms have been identified. The human PSMC3 gene has 11 exons and locates at chromosome band 19q13.11-q13.13. The human protein 26S protease regulatory subunit 6B is 47kDa in size and composed of 418 amino acids. The calculated theoretical pI of this protein is 5.09.