PA28 activator complex (also known as 11s regulator of 20S proteasome) is a ring shaped hexameric structure of alternating alpha and beta subunits. This family represents the alpha subunit. The activator complex binds to the 20S proteasome ana simulates peptidase activity in and ATP-independent manner.

1: Characterization of the mouse PA28 activator complex gene family: complete organizations of the three member genes and a physical map of the approximately 150-kb region containing the alpha- and beta-subunit genes. Kohda K, Ishibashi T, Shimbara N, Tanaka K, Matsuda Y, Kasahara M; J Immunol 1998;160:4923-4935. PMID:9590240