PARTIAL EXTRACTION OF PROTEINS FROM RAT LIVER RIBOSOMES AND PHYSICAL PROPERTIES OF RESIDUAL NUCLEOPROTEIN PARTICLES

Some of the structural proteins were detached from rat liver ribosomes by extraction with LiCl. Theresidual subribosomal particles were separated from the extracted proteins by sedimentation into 2 m sucrose. Greater amounts of the various proteins were extracted by solvents of higher LiCl concentration or higher pH. The fraction extracted in 0.5 m LiCl-0.2 mM MgCl2 at pH 7.3 contained basic proteins, which migrated rapidly in polyacrylamide gels at pH 4.5, and less basic, slow-moving proteins. Additional proteins of intermediate mobility were extracted in 0.7 or 1.0 M LiCl. Some proteins were completely removed, while others were extracted partially or not at all; a small number of proteins, of intermediate mobilities, remained bound to the residual particles. The particles remaining after extraction with 0.5 or 0.7 M LiCl were well-defined structures with sedimentation coefficients, densities, and melting-out curves that lay between those of ribosomal subunits and free ribosomal ribonucleic acids. The isolated large subunit was used to study reassociation. When the proteins extracted in 0.5 M LiCl at pH 7.3 were added back particles with a sedimentation coefficient, density, and melting-out curve like those of the isolated large subunit were recovered. © 1969, American Chemical Society. All rights reserved.