DETACHMENT OF RIBOSOMAL PROTEINS BY SALT .I. EFFECT OF CONDITIONS ON AMOUNT OF PROTEIN DETACHED

The amount of protein detached from ribosomes by salt varies markedly with the conditions used, increasing with rising salt concentration and decreasing with rising Mg2+ or ribosome concentration. The detached proteins are different from those remaining attached to the RNA. In the presence of Mg2+, where the ribosomes maintain a compact structure, the release of protein is slow and different salts have different effectivities, NaCl detaching large amounts of protein and NH4Cl none. In the absence of Mg2+, where the ribosomes are unfolded, the release is rapid and the differences among salts tend to disappear; NH4Cl is nearly as effective as NaCl. The dependence on salt and ribosome concentration remains, but the amount of protein detached from unfolded ribosomes is much greater, reaching 96% in 2 m-LiCl. Thus, nearly any desired amount of ribosomal protein can be detached by suitable manipulation of the experimental conditions. It is concluded that the conformation of the ribosome is an important factor in determining the detachment of ribosomal proteins by salt. It is also concluded that electrostatic forces have a major role in binding virtually all of the ribosomal proteins to the ribosomal RNA, and that different proteins have different affinities for the RNA. © 1969.