NMR Investigations of Fluorine-Labelled RNA: Application of Two-Dimensional Heteronuclear Experiments to Study Single-Strand Conformation

The novel application of 2D heteronuclear NMR experiments to a single-stranded RNA fragment 5′-GCAU*GGCU*ACU*U*-3′ labelled with 5-fluorouridine (U*) at four sites is reported. Heteronuclear equivalents of COSY and NOESY experiments are described, both implemented in the phase-sensitive mode. The phase-sensitive heteronuclear COSY experiment allows the observation of the 19F–1H couplings, while comparison of heteronuclear NOESY spectra at various temperatures reveals exchange phenomena, not apparent in the magnitude mode or in one-dimensional experiments. These methods and observations could have important implications for the study of conformational flexibility in larger, functionally relevant RNAs.