Formation of the First Peptide Bond: The Structure of EF-P Bound to the 70 S Ribosome

Protein Synthesis Initiation Complex The final step in the initiation phase of protein synthesis is the formation of the first peptide bond, which requires initiator transfer RNA (tRNA) to be bound at the ribosomal P site. Elongation factor P (EF-P) is a protein conserved in all eubacteria that stimulates this initial bond formation. Insight into how this is achieved comes from a structure of Thermus thermophilus 70 S ribosome bound to EF-P, initiator tRNA, and a short piece of messenger RNA presented by Blaha et al. (p. 966 ). EF-P binds between the P and E sites and facilitates proper positioning of initiator tRNA in the P site. A similar mechanism is likely to apply to structurally homologous initiation factors in archea and eukarya.