Polyribosomes, isolated from rat liver in a low ionic strength medium, capable of autonomic translation in a cell-free system without the addition of cellular fluid

Polyribosomes isolated from the liver in the presence of 10 mM KCl and purified by centrifugation through 2 M sucrose were shown to incorporate [3H]leucine both into aminoacyl-tRNA and polypeptides in a cell-free system without cell sap. The incorporation of [3H]leucine showed a linear increase within 80-100 min and was then levelled off. The system was sensitive to cycloheximide, puromycin and ethionine and needed ATP, GTP and unlabeled amino acids. The quantitation of tRNA in polyribosomes (the fraction which did not sediment with the subparticles after polyribosome dissociation) revealed more than two tRNA molecules per 80S monosome. It is likely that this tRNA excess as well as the earlier established presence of aminoacyl-tRNA synthetases and elongation factors promote the autonomic translation of polyribosomes.