Figure 3.

Miscoding by the G24A and A9C Trp-tRNA^Trp. A) Mutation of G24A (red) facilitates formation of a hydrogen bonding interaction that is not possible in native tRNA^Trp (green) between the exocylic amine of A24 and O6 of G44. This interaction is facilitated by a small shift in the RNA backbone between residues 20 to 30 and a commensurate movement between residues 9-16, B) The interaction between residues 24 and 44 in the G24A tRNA^Trp is only possible because of a base pair between residues A26-U45 in tRNA^Trp that dictates the backbone conformation in this region. In contrast, tRNA^Thr14(purple) contains two purines, G26 and G45, at these positions, which push the tRNA backbone apart and separate residues G24 and A44. That the A26-U45 base pair is not conserved even throughout bacterial tRNA^Trp further illustrates that evolution has fine-tuned each tRNA to find a unique solution to tRNA bending during decoding. (C) In native tRNA^Trp (shown in green) a base triple forms between residues 9:12:23, which is at the junction of three separate strands of the tRNA. Mutation of residue 9 to a cytosine (shown in orange) weakens both the packing and hydrogen-bonding of this base-triple, which could result in higher flexibility of the tRNA body and explain its ability to miscode.