Triple resonance experiments for the simultaneous correlation of H6/H5 and exchangeable protons of pyrimidine nucleotides in 13C,15N-labeled RNA applicable to larger RNA molecules

Triple-resonance two-dimensional H6/H5(C4N)H and C6/C5(C4N)H experiments are described that provide through-bond H6/H5 or C6/C5 to imino/amino correlations in pyrimidine bases in ¹³C,¹⁵N-labeled RNA. The experiments simultaneously transfer H6/H5 magnetization by an INEPT step to the C6/C5 nuclei and by homonuclear CC- and heteronuclear CN-TOCSY steps via the intervening C4 nucleus to the N3/N4 nuclei and then by a reverse INEPT step to the imino/amino hydrogens. The sensitivity of these experiments is high as demonstrated using a 30-nucleotide pyrimidine rich RNA at a concentration of 0.9 mM at temperatures of 10°C and 25°C. This indicates the general applicability of the experiments and the possibility to obtain correlations for imino resonances in non-canonical regions of the target RNA.