15N-, 13C-, and 31P-NMR studies of 15N-DNA in solution

The authors determined the high-resolution 15N-, 13C-, and 31P-NMR relaxation parameters in order to lend insight into the structure, dynamics and hydrogen exchange rates of uniformity-labeled 15N-DNA. Distortionless enhancement of the 15N NMR signals by polarization transfer afforded the relative rates of hydrogen exchange of the protonated nitrogens: The relative proton exchange rates for the amino groups increased from Gua = 1, Ade = 1.23, double-stranded Cyt=4.41 and single-stranded Cyt=21.7. The 13C-NMRT1's, n.O.e.'s and linewidths indicated that the planes of the bases and deoxyribosyls experienced fast motion within the DNA helix. The 13Cn.O.e. values of the protonated base carbons were close to the sugar carbon n.O.e.'s. In the 13P-NMR spectrum of the DNA, the peak representing the terminal residues resonated 3.89 ppm upfield from the internal phosphates. The 31P T1 indicated that internal motion of the DNA phosphates was independent of the overall motion of the helix