Fig. 3.

Geometry of the wobble base pair and codon•anticodon interaction. (A) The electron density shows that both the f⁵C₃₄•G₃ and f⁵C₃₄•A₃ base pairs are in Watson–Crick geometry. ASL carbons are colored green, and mRNA carbons are blue (m2F_O-dF_C contoured at 1.5 σ). (B) Superposition of the AUG complex with the AUA structure aligned with respect to the mRNA residues. The overlay reveals a nearly identical orientation of the codon•anticodon interaction between the AUA-bound and AUG-bound structures. The ASL and mRNA residues for the AUA-bound structures are green and blue, respectively. The ASL and mRNA residues of the AUG-bound structure are both gray.