TRIPLE-RESONANCE HNCCCH EXPERIMENTS FOR CORRELATING EXCHANGEABLE AND NONEXCHANGEABLE CYTIDINE AND URIDINE BASE PROTONS IN RNA

A set of triple resonance experiments is presented, providing through- bond H2N/HN to H6 connectivities in uridines and cytidines in C-13-/N- 15-labeled RNAs. These connectivities provide an important link betwee n the sequential assignment pathways for the exchangeable and nonexcha ngeable proton resonances in nucleic acids. Both 2D and pseudo-3D HNCC CH experiments were applied to a 30-nucleotide lead-dependent ribozyme , known as the leadzyme. The HN to H6 connectivities for three uridine s in the leadzyme were identified from one 2D H(NCCC)H experiment, and the H2N to H6 connectivities were identified for seven of the eight c ytidines from the combination of a 2D H(NCCC)H and a pseudo-3D H(NCC)C H experiment.