Ribosomal Subunits from Rat Liver

Large subunits from rat liver ribosomes, dialyzed against monovalent cation‐free buffer, were completely inactive in polyphenlyalanine synthesis and failed to reassociate with standard 40‐S subunits. Small subunits dialyzed under exactly the same conditions kept about 2/3 of their‐activity in poly(U)‐directed [14C]phenylalanyl‐tRNA binding or protein synthesis and could reassociate with standard 60‐S subunits. The nature of the monovalent cation present in low concentrations in the dialysis buffer was important in determining the activity of the 60‐S, but not of the 40‐S subunits: K+, Rb+ and NH+4 were more effective while Cs+, Li+ and Na+ were less effective.The various monovalent cations could be used at higher concentrations to prepare active subunits, except for Cs+ and Li+ which selectively inactivated the 60‐S subunits while modifying their conformation.Experiments with bivalent cations also showed the cationic content of the medium to be more critical for maintaining the functional form of 60‐S than of 40‐S subunits.