ИСТИНА

The molecular mechanism of protein biosynthesis is the focus of intensive studies. Termination of translation in eukaryotes is governed by the cooperative action of two interacting proteins, eRF1 and eRF3. eRF1 contains three structurally separated domains, each of which can be assigned with a specific function. The N-terminal domain is involved in the recognition of one of the three mRNA stop codons (UAA, UAG or UGA) in the decoding centre of the small ribosomal subunit. The middle (M) domain catalyses the hydrolysis of the peptidyl-tRNA ester bond within the peptidyltransferase center of the 60S ribosome subunit. The C-domain of eRF1 binds to eRF3 and this interaction increases the efficiency of translation termination. High quality structural information is essential for understanding the nature of this complex process. However atomic resolution data for eukaryotic termination complexes are unavailable; and the quality of the eRF1 crystal structure suffers from having several regions of the protein ill-defined. We determined high resolution solution structures of each domain of human eRF1 (PDB IDs: 2LLX for the N-domain, 2HST for the M-domain, 2KTV and 2KTU for two conformers of the C-domain). Clear distinctions between the protein conformations in solution and crystals were found for all the eRF1 domains, especially for their functionally important regions. The protein backbone motions were studied using 15N relaxation experiments. Heteronuclear methods were used to map the interaction interface of the M domain of the human eRF1 with eukaryotic ribosomes: the protein was found to specifically interact with the 60S subunit, since no interaction was detected with the 40S subunit. Assignments for the protein backbone signals of the full-size eRF1 (~50 kDa) have been obtained. Comparison of the NMR data for the separate domains and for the full-size protein reveals complex conformational features of the eRF1. These results complemented by the findings from molecular dynamics simulations and functional studies carried out on several eRF1 mutants provide new insights into the mechanism of translation termination in eukaryotes. Research is supported by grants from the Russian Foundation for Basic Research (10-04-13308), Medical Research Council, UK and the National Science Council, Taiwan (99-2923-B-001-005).