13C-Detection in RNA bases:: Revealing structure-chemical shift relationships

The chemical shifts of the unprotonated carbons in the proton-deficient nucleobases of RNA are rarely reported, despite the valuable information that they contain about base-pairing and base-stacking. We have developed C-13-detected 2D-experiments to identify the unprotonated C-13 in the RNA bases and have assigned all the base nuclei of uniformly. C-13, N-15-labeled HIV-2 TAR-RNA. The C-13 chemical shift distributions revealed perturbations correlated with the base-pairing and base-stacking properties of all four base-types. From this work, we conclude that the information contained in the chemical shift perturbations within the base rings can provide valuable restraint information for solving RNA structures, especially in conformational averaged regions, where NOE-based information is not available.