The proteasome 11S regulator subunit REGα (PA28α) is a heptamer

Abstract
Activity of the 20s proteasome, which performs much of the cytosolic and nuclear proteolysis in eukaryotic cells, is controlled by regulatory complexes that bind to one or both ends of the cylindrical proteasome. One of these complexes, the 11S regulator (REG), is a complex of 28 kDa subunits that is thought to activate proteasomes toward the production of antigenic peptides. REG, purified from red blood cells, is a complex of REGα and REGβ subunits. We have crystallized recombinant REGα (rREGα) and collected diffraction data to 3.0 Å resolution. The self-rotation function indicates that rREGα forms a heptameric ring in the crystal. Equilibrium sedimentation demonstrates that rREGα is a heptamer in solution also.