Stabilizes the proteasome holoenzyme, probably by tethering the 20S proteolytic core particle and the 19S regulatory particle. The proteasome is a multicatalytic proteinase complex which is characterized by its ability to cleave peptides with Arg, Phe, Tyr, Leu, and Glu adjacent to the leaving group at neutral or slightly basic pH. The proteasome has an ATP-dependent proteolytic activity (By similarity). Component of the proteasome. Belongs to the ECM29 family.