Figure 8.

Comparison of residues 31–39 of (A) the solution structure of E.coli tRNA^Phe (42) and the crystal structures of (B) fully modified yeast tRNA^Phe (15,16) and (C) fully modified tRNA^Asp (18,21). ψ₃₂ and A₃₈ in (A) form a Watson–Crick base pair. In (B) and (C), nucleotides C₃₂-A₃₈ and ψ₃₂-C₃₈, respectively, form the bifurcated hydrogen bond. The anticodon loop in (A) adopts the tri-loop conformation whereas the anticodon loops in (B) and (C) adopt the U-turn motif. In E.coli tRNA_Cys, ψ₃₂ is in the syn configuration about the glycosidic bond and the loop forms a U-turn motif (17).