Interaction of tRNA with the A and P sites of rabbit-liver 80S ribosomes and their 40S subunits.

The interaction between tRNA and rabbit liver 80S ribosomes and 40S subunits was studied using a nitrocellulose membrane filtration technique. Binding of the different tRNA forms (aminoacyl-, peptidyl- or deacylated) to poly(U)-programmed 40S subunits and 80S ribosomes was found to be a cooperative process. The association constants of AcPhe-TRNA(Phe) for the A and P sites of 80S ribosomes and the cooperativity constant were measured at different temperature and Mg2+ concentration. The AcPhe-tRNA(Phe) association constant for the P site was shown to be between 2 x 10(7) M-1 and 2 x 10(8) M-1 at 25-37 degrees C and 5-20 mM Mg2+, while the affinity for the A site was 10-100-fold lower. The cooperativity constant was shown to decrease with the increase of incubation temperature and the decrease of Mg2+ concentration. The affinity of AcPhe-tRNA(Phe) for the A site of 80S ribosomes was shown to depend upon the codon specificity of tRNA at the P site. The cooperativity of the tRNA interaction with 80S ribosomes was suggested to be mostly contributed by the association with the 40S subunit and result from the correct codon-anticodon pairing at the P site. The data presented imply a codon-anticodon interaction at the P site of eukaryotic 80S ribosomes.