Influence of the hypermodified Y base on the A·U pairing in the codon–anticodon interaction

Through AM1 calculations we show that, when the first uracil of codon UUC binds to A36 of anticodon GAA of tRNAPhe, dramatic conformational variations occur in the side chain of the hypermodified Y base in position 37. The H-bond found, involving one of the Y side-chain carboxylic oxygens and one of the A36 amino hydrogens, confers to A·U the stabilization energy of G·C. The calculated group-group indices and molecular valences agree with these features. We suggest that this stabilization of A·U, due to the presence of the Y base, may prevent misreading in the genetic code.