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The decoding of mRNA on the ribosome is the least accurate process during genetic information transfer. Here we propose a unified decoding mechanism based on 11 high-resolution X-ray structures of the 70S ribosome that explains the occurrence of missense errors during translation. We determined ribosome structures in rare states where incorrect tRNAs were incorporated into the peptidyl-tRNA-binding site. These structures show that in the codon–anticodon duplex, a G·U mismatch adopts the Watson–Crick geometry, indicating a shift in the tautomeric equilibrium or ionization of the nucleobase. Additional structures with mismatches in the 70S decoding centre show that the binding of any tRNA induces identical rearrangements in the centre, which favours either isosteric or close to the Watson–Crick geometry codon–anticodon pairs. Overall, the results suggest that a mismatch escapes discrimination by preserving the shape of a Watson–Crick pair and indicate that geometric selection via tautomerism or ionization dominates the translational infidelity mechanism., Translation of mRNA into proteins is the least accurate process during genetic information transfer. Here the authors suggest—based on 11 high-resolution ribosome crystal structures—that the origin of protein missense errors involves molecular mimicry via tautomerism or ionization.

Eukaryotic ribosomal proteins, unlike their bacterial homologues, possess nuclear localization signals (NLSs) to enter the cell nucleus during ribosome assembly. Here we provide a comprehensive comparison of bacterial and eukaryotic ribosomes to show that NLSs appear in conserved ribosomal proteins via remodelling of their RNA-binding domains. This finding enabled us to identify previously unknown NLSs in ribosomal proteins from humans, and suggests that, apart from promoting protein transport, NLSs may facilitate folding of ribosomal RNA., Eukaryotic ribosomal proteins contain nuclear localization signals (NLSs) that their bacterial counterparts lack. Here the authors compare homologous proteins from bacterial and eukaryotic ribosomes to show how NLSs could emerge in the course of evolution, and use this knowledge to identify novel NLSs.