Ribosomes and microsomes isolated from the livers of rats that had received carbon tetrachloride 1hr. previously had decreased endogenous capacity to incorporate amino acid. 2. The capacity of the isolated structures to respond to a synthetic messenger, polyuridylic acid, and to incorporate phenylalanine was investigated. 3. It was found that ribosomes from carbon tetrachloride-treated animals, prepared with detergent and at high ionic strength, could be restored to the same specific activity as control particles with polyuridylic acid but that these particles required more Mg(2+) in the incubation mixture. 4. Microsomes could also be stimulated to control activities with polyuridylic acid, but had a narrow optimum range of Mg(2+) concentration. 5. Microsomes prepared from poisoned animals could be preprogrammed with polyuridylic acid to a significantly greater degree than could control particles, and this response was greater with increasing Mg(2+) concentrations. These data suggested that in carbon tetrachloride poisoning the messenger-ribosome interaction had been altered. 6. Attempts to deprogramme particles from control and treated animals resulted in decreased endogenous activity of both particles and a decreased capacity for the treated particles to be restored with the synthetic messenger. 7. It is suggested that two effects are present in carbon tetrachloride poisoning, namely an alteration of the messenger-ribosome interaction and an increased lability of the ribosome, as either separate or related events.
