NMR spectroscopic determination of angles alpha and delta in RNA from CH-dipolar coupling, P-CSA cross-correlated relaxation

A new method is introduced to measure the backbone torsion angles alpha and zeta in C-13-labeled oligonucleotides. The experiments relies on the quant ification of the cross-correlated relaxation of C,P double and zero quantum coherence caused by the C,H dipolar coupling and the P chemical shift anis otropy. Two-dimensional surfaces that reveal the angular dependence of the cross-correlated relaxation rates depend on the backbone angles alpha and b eta as well as epsilon and zeta and are interpreted using torsion angle inf ormation for the angles beta and epsilon from experiments measuring (3)J(H, P) and (3)J(C,P) coupling constants. The experiments have been carried out on the 10mer RNA 5'-CGCUUUUGCG-3' that forms a hairpin and in which the fou r uridine residues are C-13-labeled in the ribofuranoside moiety.