RESUMO
Termination of translation in eukaryotes is governed by two polypeptide chain release factors. The middle (M) domain of the class 1 translation termination factor eRF1 contains the strictly conserved GGQ motif and involved in hydrolysis of the peptidyl-tRNA ester bond within the peptidyl transferase center of the large ribosome subunit. Heteronuclear NMR spectroscopy was used to map the interaction interface of the M-domain of human termination factor eRF1 with eukaryotic ribosomes. The protein was found to interact specifically with the large 60S ribosomal subunit: no interaction was detected between the M-domain of eRF1 and the 40S ribosomal subunit. The protein residues at the interaction interface are mainly situated on the long alpha-helix, alpha1 of the M-domain. Some residues adjacent to alpha1, in strand beta5, and in two short helices alpha2 and alpha3 are also involved in the protein-ribosome contact. The interaction of the functionally inactive mutant G183A with the 60S ribosomal subunit is substantially weaker than that found for the wild-type protein. Moreover, the interaction interfaces are not identical in these two cases. The results highlight the functional importance of the long alphal helix and also indicate that conformational flexibility of the GGQ loop is essential for forming tight protein-ribosome contacts.
