Recognition of a start codon by the initiator aminoacyl-tRNA determines the reading frame of messenger RNA (mRNA) translation by the ribosome. In eukaryotes, the GTPase eIF5B collaborates in the correct positioning of the initiator Met-tRNA i Met on the ribosome in the later stages of translation initiation, gating entrance into elongation. Leveraging the long residence time of eIF5B on the ribosome recently identified by single-molecule fluorescence measurements, we determine the cryoEM structure of the naturally long-lived ribosome complex with eIF5B and Met-tRNA i Met immediately before transition into elongation. The structure uncovers an unexpected, eukaryotic specific and dynamic fidelity checkpoint implemented by eIF5B in concert with components of the large ribosomal subunit.
Organizational Affiliation:
Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA.
Department of Biochemistry and Molecular Biophysics, Columbia University, New York City, NY, USA.
Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD, USA.
Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD, USA. thomas.dever@nih.gov.
Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA. puglisi@stanford.edu.
Department of Biochemistry and Molecular Biophysics, Columbia University, New York City, NY, USA. isf2106@cumc.columbia.edu.
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