Through-bond correlation of imino and aromatic resonances in 13C-, 15N-labeled RNA via heteronuclear TOCSY.

Novel HCCNH TOCSY NMR experiments are presented that provide unambiguous assignment of the exchangeable imino proton resonances by intranucleotide through-bond connectivities to the (assigned) nonexchangeable purine H8 and pyrimidine H6 protons in uniformly 15N-, 13C-labeled RNA oligonucleotides. The HCCNH TOCSY experiments can be arranged as a two-dimensional experiment, correlating solely GH8/UH6 and GH1/UH3 proton resonances (HCCNH), 51 as three-dimensional experiments, in which additional chemical shift labeling either by GN1/UN3 (HCCNH) or by GC8/UC6 (HCCNH) chemical shifts is introduced. The utility of these experiments for the assignment of relatively large RNA oligonucleotides is demonstrated for two different RNA molecules.