A ribosome dissociation factor from rabbit reticulocytes distinct from initiation factor M3.

A ribosome dissociation factor (DF), from a 0.5 M KCl wash fraction of rabbit-reticulocyte-ribosomes, has been purified by Sephadex G-200, phosphocellulose, DEAE-cellulose, and hydroxyapatite chromatography. The most purified preparation displayed one major and several minor bands on 3.75% acrylamide gels.DF cannot replace IF-M(1), IF-M(2A), IF-M(2B), IF-M(2), EF-1, or EF-2 in poly(U)-directed polyphenylalanine synthesis at low Mg(++) concentrations or in endogenous mRNA-directed globin synthesis. Conversely, these initiation and elongation factors showed little or no dissociation activity, even when assayed at levels 5-10 times greater than those required to saturate a polypeptide synthesis assay. Reticulocyte DF thus appears to be a distinct factor.