Localization of subunits in proteasomes from <i>Thermoplasma acidophilum</i> by immunoelectron microscopy

Abstract

The subunit topography of the Thermoplasma acidophilum proteasome was determined by immunoelectron microscopy using monospecific antibodies directed against the two constituent subunits (alpha,beta). Anti-alpha-subunit IgG was found to bind to the outer disks of the cylinder- or barrel-shaped molecule, while the binding sites of the anti-beta-subunit IgG were mapped on the two inner rings. Probably the homologues of the two subunits in the compositionally more complex but isomorphous eukaryotic proteasomes occupy equivalent positions.