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Summary 80S ribosomes from skeletal muscle of diabetic rats were more susceptible than normal to dissociation by the initiation factor EIF-3; the increased sensitivity to dissociation was a property of the 60S subunit. Increased dissociation may be a reflection of the instability of diabetic 80S couples resulting from a change in the structure of the large subunit.

The effect of various sulfhydryl reagents on the ribosomes of Bacillus subtilis was studied. The 70 S ribosomes were completely dissociated into 30 S and 50 S subunits by appropriate concentrations of p -chloromercuribenzoic acid (PCMB) and 5,5′-dithio- bis -(2-nitro-benzoic acid). The N -ethylmaleimide and iodoacetamide failed to dissociate the ribosomes even at relatively high concentrations. The rate of dissociation of ribosomes by PCMB varied with the concentration of ribosomes. A progressive decrease in the rate of dissociation was observed as the concentration of ribosomes in the reaction mixture was increased. The PCMB-induced ribosomal subunits were unable to reassociate into 70 S monomers unless they were dialyzed against buffer containing β-mercaptoethanol. On the average, four molecules of PCMB per 70 S ribosome and two molecules of PCMB per each 30 S and 50 S subunit were bound. The number of PCMB molecules bound per ribosome did not change with increasing concentrations of PCMB, even though higher concentrations of PCMB resulted in dissociation of ribosomes into subunits.

Purified eukaryotic initiation factor, EIF-3, prepared from ascites cells dissociated rat liver 80S ribosomes into subunits. Ribosomes bearing endogenous mRNA and nascent peptide were not dissociated by EIF-3. When 80S ribosomes reconstituted from subunits were used as substrate the reaction had the following characteristics: Dissociation was rapid--the reaction being completed within 2 min at 30°. The extent of dissociation was directly proportional to the amount of EIF-3; with 21 μg of EIF-3 about 70% (or 10.5 μg) of the 80S monomers were dissociated. The dissociation of 80S monomers by EIF-3 decreased with increasing concentrations of magnesium. The reaction was not catalytic: 28 moles of EIF-3 were required to dissociate 1 mole of 80S ribosomes. The characteristic of the dissociation reaction promoted by EIF-3 and by E. coli initiation factor IF-3 are remarkably similar. The dissociation reaction provides a practical assay for EIF-3 independent of complimentation of other initiating factors.

The biological activities of Bacillus subtilis ribosomes pretreated with 0.5, 1, or 2 m m p -chloromercuribenzoate (PCMB) were examined. The ribosomes treated with 1 or 2 m m PCMB lost their capacity to synthesize polyphenylalanine as well as the capacity to bind phenylalanyl-transfer ribonucleic acid. On the other hand, approximately 70% of the polyphenylalanine synthesis capacity was lost with ribosomes pretreated with 0.5 m m PCMB. This inhibition was found to be due to a specific inhibition of the translocation step. The effect of 0.5 m m PCMB was reversed by 20 m m Mg 2+ without the loss of PCMB bound to ribosomes, while β-mercaptoethanol partially reversed the inhibitory effect with concomitant loss of bound PCMB.

Tanned sheep erythrocytes have been considered incapable of sensitization with the precipitinogen of protein A of Staphylococcus aureus , so that the activity of this antigen in serological reactions has so far been studied by means of the agar diffusion test (ADT) only. The precipitinogen of the protein A in this study was found to become attached to the tanned erythrocytes and to sensitize them for the passive hemagglutination test (PHT). It was determined that, in contrast to nonspecific reactivity between normal human serum and the precipitinogen in the ADT, the reaction in the PHT was of specific nature. Of seven species studied, all normal human, dog, and hog sera tested were positive in the PHT. However, the hemagglutinin titers of the sera of the two animal species by far exceeded those of the human sera. The data emphasized the usefulness of the highly sensitive PHT for assaying antibodies to protein A.