Subunit of the 11S REG (also called PA28) proteasome regulator, a doughnut-shaped homoheptamer which associates with the proteasome. 11S REG-gamma activates preferentially the trypsin-like catalytic subunit of the proteasome. May also be involved in cell cycle regulation. Homoheptamer. The homoheptamer associates with the 20S proteasome. Belongs to the PA28 family.