4D Non-uniformly sampled C,C-NOESY experiment for sequential assignment of 13C,15N-labeled RNAs

A 4D C-13(aromatic),C-13(ribose)-edited NOESY experiment is introduced to improve sequential assignment of non-coding RNA, often hampered by a limited dispersion of H-1 and C-13 chemical shifts. The C-13-labeling of RNA is fully utilized by inclusion of two C-13 evolution periods. These dimensions provide enhanced dispersion of resonances in the 4D spectrum. High spectral resolution is obtained using random non-uniform sampling in three indirect dimensions. The autocorrelation peaks are efficiently suppressed using band-selective pulses. Since the dynamic range of observed resonances is significantly decreased, the reconstruction of the 4D spectrum is greatly simplified. The experiment can replace two conventionally sampled 3D NOESY spectra (either ribose-C-13- or aromatic-C-13-separated), and remove most ambiguities encountered during sequential walks. The assignment strategy based on a homonuclear and 4D C,C-edited NOESY experiments is proposed and verified on a 34-nt RNA showing typical structure elements.