Characterization of Eukaryotic Release Factor 3 (eRF3) Translation Termination Factor in Plants

Eukaryotic translation termination is mediated by two conserved interacting release factors, eRF1 and eRF3. eRF1 recognizes the stop codon and promotes the hydrolysis of the polypeptide chain, while eukaryotic eRF3 stimulates eRF1 release activity in the presence of GTP. It is widely believed that translation termination is highly conserved in eukaryotes. However, recent results that eRF1 is present in multiple, partially redundant copies in plants and that eRF1 expression is controlled by a complex, plant-specific autoregulatory circuit suggest that regulation of translation termination might be especially complex in plants. Surprisingly, very little is known about translation termination in plant, for instance, the eRF3 termination factor has not been analyzed in plants yet. Thus, we wanted to identify and characterize the eRF3 translation termination factor in plants. By combining a range of transient and transgenic assay here, we identified plant eRF3 and showed that it directly interacts with eRF1. In contrast to eRF1, plant eRF3 is not autoregulated, while eRF3 and eRF1 expressions are connected. We also demonstrated that eRF3 interacts with the core NMD factor, UPF1, and the expression of eRF3 is NMD regulated in certain plant species suggesting that in addition to the normal translation termination, eRF3 could be connected to plant nonsense-mediated decay (NMD). Finally, it appears that the plant termination factors are present in physiologically different concentrations, while eRF1 concentration limits the efficiency of both translation termination and NMD, eRF3 is present in non-limiting concentration.