passages.id: split_4_test_581_passage
passages.type: progene_text
passages.text: The complex is composed of two relatively stable subparticles , the 20S proteasome , a hollow cylindrical structure which contains the proteolytic active sites in its lumen , and the 19S regulatory particle ( RP ) which binds to either end of the cylinder and provides the ATP - dependence and the specificity for ubiquitinated proteins .