Messenger RNA conformations in the ribosomal E site revealed by X-ray crystallography

A comparison of messenger RNA in X-ray crystal structures of 70S ribosomal complexes in the initiation, post-initiation and elongation states of translation shows distinct conformational differences in the exit (E) codon. Here, we present structural evidence indicating that, after the initiation event, the E codon nucleotides relax and form a classical A-helical conformation. This conformation is similar to that of the P and A codons, and is favourable for establishing Watson-Crick interactions with the anticodon of E-site transfer RNA.