Crystal Structure of the Eukaryotic Ribosome

Macromolecular Message Translation The ribosome is a macromolecular machine that translates the sequence of messenger RNA into proteins in all living cells. Structures of prokaryotic ribosomes have supplied insight into the conserved features of such protein synthesis; however, eukaryotic translation has additional levels of complexity. Ben-Shem et al. (p. 1203) have determined the crystal structure of the yeast 80S ribosome at 4.15 angstrom resolution. The ribosome is in a ratcheted conformation, which is a state that is an intermediate in the translocation of messenger RNA and transfer RNA. The crystal structure provides the molecular underpinning for existing biochemical and genetic data and will inform the design of functional experiments. The structure of the 80S ribosome from yeast has been determined at 4.15 angstrom resolution. Crystal structures of prokaryotic ribosomes have described in detail the universally conserved core of the translation mechanism. However, many facets of the translation process in eukaryotes are not shared with prokaryotes. The crystal structure of the yeast 80S ribosome determined at 4.15 angstrom resolution reveals the higher complexity of eukaryotic ribosomes, which are 40% larger than their bacterial counterparts. Our model shows how eukaryote-specific elements considerably expand the network of interactions within the ribosome and provides insights into eukaryote-specific features of protein synthesis. Our crystals capture the ribosome in the ratcheted state, which is essential for translocation of mRNA and transfer RNA (tRNA), and in which the small ribosomal subunit has rotated with respect to the large subunit. We describe the conformational changes in both ribosomal subunits that are involved in ratcheting and their implications in coordination between the two associated subunits and in mRNA and tRNA translocation.