Fig. 1

The 26S proteasome is composed of one proteolytically active cylinder-shaped particle (the 20S proteasome) and ATPase-containing complexes (the 19S cap complexes). The 19S cap complex unfolds ubiquitin-conjugated proteins to allow their entry into the 20S cylindrical particle. The 19S regulatory particles on the ends of the 20S proteasome are composed of at least 18 subunits. The base contains the two largest subunits of the proteasome, Rpn1 and Rpn2, the ubiquitin receptor Rpn10 and Rpn13, and the six ATPases, Rpt1-Rpt6. 19S RP, 19S regulatory particle. 20S CP, 20S core particle