DIFFERENCE BETWEEN PA700-LIKE PROTEASOME ACTIVATOR COMPLEX AND THE REGULATORY COMPLEX DISSOCIATED FROM THE 26S PROTEASOME IMPLIES THE INVOLVEMENT OF MODULATING FACTORS IN THE 26S PROTEASOME ASSEMBLY

The PA700-like proteasome activator complex was highly purified from p orcine erythrocytes, and its properties were compared with those of th e regulatory complex disassembled from the purified 26S proteasome. Th e molecular mass of the PA700-like complex, which comprises 25-110-kDa subunits, was estimated to be 800 kDa by Superose 6 gel filtration, T his complex showed neither ATPase activity nor peptidase activity towa rd Suc-Leu-Leu-Val-Tyr-MCA. Nevertheless, it was possible to make a hi gh molecular mass complex from the purified PA700-like complex by incu bating with the 20S proteasome in the presence of ATP. In contrast, th e regulatory complex dissociated from the 26S proteasome did not recon stitute a larger complex under the same conditions, The subunit compos ition of the PA700-like complex was similar but not identical to that of the regulator complex dissociated from the 26S proteasome: the form er complex had a 25-kDa subunit which is, absent in the latter, wherea s the latter had two or three 43-kDa subunits lacking in the former, T hese results indicate that the purified PA700-like proteasome activato r complex is structurally and functionally distinct from the regulator y complex dissociated from the 26S proteasome, implying the involvemen t of modulating factors in the 26S proteasome assembly. (C) 1997 Feder ation of European Biochemical Societies.