Structures of Yeast 80S Ribosome-tRNA Complexes in the Rotated and Nonrotated Conformations

The structural understanding of eukaryotic translation lags behind that of translation on bacterial ribosomes. Here, we present two subnanometer resolution structures of S. cerevisiae 80S ribosome complexes formed with either one or two tRNAs and bound in response to an mRNA fragment containing the Kozak consensus sequence. The ribosomes adopt two globally different conformations that are related to each other by the rotation of the small subunit. Comparison with bacterial ribosome complexes reveals that the global structures and modes of intersubunit rotation of the yeast ribosome differ significantly from those in the bacterial counterpart, most notably in the regions involving the tRNA, small ribosomal subunit, and conserved helix 69 of the large ribosomal subunit. The structures provide insight into ribosome dynamics implicated in tRNA translocation and help elucidate the role of the Kozak fragment in positioning an open reading frame during translation initiation in eukaryotes. •80S ribosomes bound with tRNAs in the classical E and P site adopt a nonrotated state•The small subunit of the 80S ribosome bound with single P/E tRNA is rotated by ∼8.5°•The conformations of the small subunit and tRNAs differ between 70S and 80S ribosomes•The conserved −3 purine of the Kozak sequence helps position the AUG codon in the P site Svidritskiy et al. report molecular structures of tRNA-bound eukaryotic ribosomes. The structures shed light on the role of the conserved mRNA Kozak sequence in positioning the AUG start codon at the start of translation. They also reveal ribosome and tRNA rearrangements involved in tRNA movement within the ribosome.