Structural insights into eukaryotic ribosomes and the initiation of translation

The initiation of protein biosynthesis entails the ordered assembly of elongation-competent ribosomes, with an initiator tRNA basepaired to an appropriate mRNA start codon. In eukaryotes, this process is more complex than in prokaryotes and involves numerous protein factors that mediate tRNA delivery, mRNA binding, start codon selection and subunit joining. The recent 40S:eIF1, 80S and eIF2:tRNA:GDPNP ternary complex structures provide an initial structural framework toward a molecular understanding of the eukaryotic translation initiation process. Updated homology models of larger initiation complexes provide first insights into the likely arrangements of these higher-order complexes, but also reveal the limits of our current understanding of the eukaryotic translation initiation process.