Structural basis of highly conserved ribosome recycling in eukaryotes and archaea

Ribosome-driven protein biosynthesis is comprised of four phases: initiation, elongation, termination and recycling. In bacteria, ribosome recycling requires ribosome recycling factor and elongation factor G, and several structures of bacterial recycling complexes have been determined. In the eukaryotic and archaeal kingdoms, however, recycling involves the ABC-type ATPase ABCE1 and little is known about its structural basis. Here we present cryo-electron microscopy reconstructions of eukaryotic and archaeal ribosome recycling complexes containing ABCE1 and the termination factor paralogue Pelota. These structures reveal the overall binding mode of ABCE1 to be similar to canonical translation factors. Moreover, the iron–sulphur cluster domain of ABCE1 interacts with and stabilizes Pelota in a conformation that reaches towards the peptidyl transferase centre, thus explaining how ABCE1 may stimulate peptide-release activity of canonical termination factors. Using the mechanochemical properties of ABCE1, a conserved mechanism in archaea and eukaryotes is suggested that couples translation termination to recycling, and eventually to re-initiation. Cryo-electron-microscopy reconstructions of eukaryotic and archaeal ribosomes bound by ABCE1 and Pelota suggest a conserved mechanism for ribosome recycling. The round trip for ribosomes Once a ribosome completes translation of an RNA messenger, it must recycle itself by dissociating its large and small subunits. In archaea and eukaryotes, the ABCE1 protein promotes recycling in combination with termination release factors. Roland Beckmann and colleagues have performed cryoelectron-microscopy reconstructions of the eukaryotic and archaeal ribosomes bound by ABCE1 and Pelota, an mRNA surveillance factor that is a paralogue of release factors. They find that ABCE1 binds between the two subunits, and that its iron–sulphur domain places Pelota in a conformation that promotes peptide release by canonical release factors. This work suggests a remarkable degree of structural and functional conservation over the more than one billion years of evolution that separates eukaryotes and archaea. The observed ribosomal structures suggest a model for an ATP-driven power stroke that would disassemble the subunits.