Proteasome activator complex subunit 3 (PSME3),a member of the PA28 family, is also known as 11S regulator complex subunit gamma (REG-gamma), activator of multicatalytic protease subunit 3 and proteasome activator 28 subunit gamma (PA28gamma). PSME3 activates the trypsin-like catalytic subunit of the proteasome but inhibits the chymotrypsin-like and postglutamyl-preferring (PGPH) subunits. PSME3 can also facilitate the MDM2-p53/TP53 interaction which promotes ubiquitination- and MDM2-dependent proteasomal degradation of p53/TP53, limiting its accumulation and resulting in inhibited apoptosis after DNA damage. Furthermore,PSME3 may also be involved in cell cycle regulation.