Evidence indicating that the human proteasome is a complex dimer.

Using monoclonal antibodies and electron microscopy, the relative positions of two subunit species (32 kDa, pI 6.8; 28.4 kDa, pI 7.9) have been determined on the proteasome (multicatalytic proteinase). From the epitope occupancy, it appears that both subunits occur twice in a proteasome: once in each of the two terminal disks that close off the barrel-like particle. The result favors a model of a complex dimer, and is discussed in the light of the architectural concept that has emerged from our recent immunoelectron microscopic studies of the less complex archaebacterial proteasome.