THE HUMAN PROTEASOME SUBUNIT HSN3 IS LOCATED IN THE INNER RINGS OF THE COMPLEX DIMER

Subunit HsN3 of the human proteasome is a beta-type subunit homologous to PRE4 from yeast, X1 beta from Xenopus and RN3 from the rat. Using electron microscopy, the binding sites of a monoclonal antibody with s pecificity for subunit HsN3 have been located in the two juxtaposed in ner rings of the human proteasome. Subunit HsN3 was present in two cop ies, one in each ring, in accordance with our concept of two identical halves making up the complete human proteasome. The subunit is involv ed in the trypsin-like as well as the peptidylglutamyl-peptide cleavag e activities.