Abstact

Termination and ribosome recycling are essential processes in translation. In eukaryotes, a stop codon in the ribosomal A site is decoded by a ternary complex consisting of release factors eRF1 and guanosine triphosphate (GTP)-bound eRF3. After GTP hydrolysis, eRF3 dissociates, and ABCE1 can bind to eRF1-loaded ribosomes to stimulate peptide release and ribosomal subunit dissociation. Here, we present cryoelectron microscopic (cryo-EM) structures of a pretermination complex containing eRF1-eRF3 and a termination/prerecycling complex containing eRF1-ABCE1. eRF1 undergoes drastic conformational changes: its central domain harboring the catalytically important GGQ loop is either packed against eRF3 or swung toward the peptidyl transferase center when bound to ABCE1. Additionally, in complex with eRF3, the N-terminal domain of eRF1 positions the conserved NIKS motif proximal to the stop codon, supporting its suggested role in decoding, yet it appears to be delocalized in the presence of ABCE1. These results suggest that stop codon decoding and peptide release can be uncoupled during termination.