The Controlled Dissociation of Proteins from Rat Liver Ribosomes by Potassium Chloride

Up to 50% of the protein was dissociated from rat liver ribosomes when they were zonally centrifuged through a solution containing KCl in concentrations up to 1.0 M. Sucrose gradient analysis of the resulting particles showed subunits whose sedimentation rate decreased in a characteristic manner as the KCl concentration used to produce them increased. The large subunit in particular showed apparently discontinuous changes in sedimentation behaviour, suggestive of transitions from one discrete state to another. Further evidence for the existence of well‐defined protein‐deficient states was obtained by isopyenic centrifugation of the subunits in CsCl gradients after formaldehyde fixation. These showed that a spectrum of protein‐deficient particles with characteristic buoyant densities could be obtained from each subunit: treatment with KCl resulted in a mixture of these whose composition was a function of the KCl concentration. Electrophoretic analysis on polyacrylamide gels of the proteins released and those remaining on the subunits showed that the removal of proteins was selective and the quantitative increase in proteins removed with increasing KCl concentration was accompanied by greater heterogeneity. It is suggested that removal of protein from rat liver ribosomes is an ordered, stepwise phenomenon similar to that observed in bacterial ribosomes treated with CsCl or LiCl.