Proteasome activator complex subunit 2 (PSME2), a member of the PA28 family, is also known as 11S regulator complex subunit beta (REG-beta), activator of multicatalytic protease subunit 2 and proteasome activator 28 subunit beta (PA28b). PSME2 can form heterodimer with PSME1. PSME2 is implicated in immunoproteasome assembly and required for efficient antigen processing. The PA28 (PSME2) activator complex enhances the generation of class I binding peptides by altering the cleavage pattern of the proteasome.