The effect of incubation with puromycin on the dissociation of rat liver ribosomes into active subunits

In sharp contrast to polyribosomes or monomeric ribosomes produced by ribonuclease treatment of polyribosomes, ribosomes which were incubated in the presence of soluble factors, an energy generating system, and puromycin were completely dissociated into subunits when equilibrated with Tris-HCl, pH 7.8 (0.05 M), KCl (0.15 M), MgSO₄ (l.0 mM). When separated on a sucrose density gradient, these subunits did not incorporate amino acids into protein when they were tested individually. The recombined subunits were active in phenylalanine incorporation with an absolute requirement for added messenger RNA (poly U). Results obtained from these experiments support the conclusion that a major difference between 70S and 80S ribosomes may be related to the greater degree of stability conferred on the 80S subunit couple by the presence of the peptidyl-transfer RNA.