Fluorine-19 nuclear magnetic resonance study of codonanticodon interaction in 5-fluorouracil-substituted E. coli transfer RNAs

Codonanticodon interaction was investigated in fully active 5-fluorouracil-substituted E. coll tRNA^Yal (anticodon FAC) by 19^F NMR spectroscopy. Binding of the codon G_pU_pA results in the upfield shift of a ¹⁹F resonance at 3.9'ppm in the central region of the ¹⁹F NMR spectrum, whereas trinucleotides not complementary to the anticodon have no effect. The same ¹⁹F resonance shifts upfield upon formation of an anticodon-anticodon dimer between the ¹⁹F-labeled tRNA and E. coll tRNA₂^Tyr (anticodon QUA). These results permit assignment of the peak at 3.9 ppm to the 5-fluorouracil at position 34 in the anticodon of fluorouracil-substituted tRNA₁^Ya1. The methionine codon A_pU_pG also causes a sequence-specific upfield shift of a peak in the central part of the ¹⁹F NMR spectrum of fluorinated E. coli tRNA_m^Met. However, A_pU_pG has no effect on the ¹⁹F spectrum of ¹⁹F-labeled E. coli tRNA_r^Met, indicating possible conformational differences between the anti-codon loop of initiator and chain-elongating methionine tRNAs. ¹⁹F NMR experiments detect no binding of C_pG_pA_pA to the complementary F_pF_pC_pG (replaces T_pψ_pC^pG) in the T-loop of 5-fluorouracil-substituted tRNA₁^Yal, in the presence or absence of codon, suggesting that the tertiary interactions between the T- and D-loops are not disrupted by codon-anticodon interactions.