Structure of a human 48 S translational initiation complex

Finding the start Eukaryotic translation involves many players in a dynamic and well-orchestrated process. A 43 S preinitiation complex (PIC) comprises the 40 S ribosomal subunit; initiation factors, including the eIF3 complex, which is known to play a key role; and the transfer RNA used for translation initiation. The PIC is recruited to the cap-binding complex eIF4F at the 5′ end of messenger RNA (mRNA) to form a 48 S complex that scans along the mRNA for a start codon. Brito Querido et al. determined the structure of a reconstituted human 48 S complex using cryo–electron microscopy. They found that eIF4F binds to eIF3 near the exit site of the ribosome. This positioning suggests that downstream mRNA is likely pulled through the 40 S subunit to find the start codon. Science , this issue p. 1220