Binding of Ribosomes to Intramembrane Particles of Rough Microsomes. An Electron-Microscope Study

Abstract

When rat-liver rough microsomes were treated with 1.0% Triton X-100, the resulting polyribosomes were found to be still in association with membrane-like fragments or vesicles. Freeze-fracture studies of these membranous structures revealed no broad fracture faces of the lipid bilayer, but showed only a few 8 to 10nm-diameter particles similar to intramembrane particles, arranged in rows, clusters, or circles on the surface of the replica. A protein fraction solubilized from the membranous structures by sodium deoxycholate was reincorporated into artificial lipid vesicles by the detergentdialysis method. While protein-free liposomes did not bind ribosomes, the protein-containing ones bound ribosomes at 0°C. The cross-section of a vesicle recombined with ribosomes resembled that of a native hepatic rough microsome in thin section. The presence of the intramembrane particles in the protein-containing liposomes was shown by freeze-fracture techniques.