THE PROTEASOME 11S REGULATOR SUBUNIT REG-ALPHA (PA28-ALPHA) IS A HEPTAMER

Activity of the 20S proteasome, which performs much of the cytosolic a nd nuclear proteolysis in eukaryotic cells, is controlled by regulator y complexes that bind to one or both ends of the cylindrical proteasom e. One of these complexes, the 11S regulator (REG), is a complex of 28 kDa subunits that is thought to activate proteasomes toward the produ ction of antigenic peptides. REG, purified from red blood cells, is a complex of REG alpha and REG beta subunits. We have crystallized recom binant REG alpha (rREG alpha) and collected diffraction data to 3.0 An gstrom resolution. The self-rotation function indicates that rREG alph a forms a heptameric ring in the crystal. Equilibrium sedimentation de monstrates that rREG alpha is a heptamer in solution also.