Deoxyribonucleic acid dynamics from phosphorus-31 nuclear magnetic resonance

31P NMR of native high molecular weight DNA shows that the phosphodiester backbone undergoes reorientation with a rotational correlation time of about 2 X 10(-6) s at 30 degrees C. This rate is consistent with the flexibility of the polymer and does not require the presence of internal phosphate motions. The line width of the phosphorus resonance of DNA is due to incompletely averaged 31P-1H dipolar couplings and 31P chemical shift anisotropy relaxation; high-power proton decoupling and magnetic field dependence experiments separate the two effects and allow the use of the line width for determination of the rotational correlation time. The line width is dependent on temperature, and an activation energy of 5-8 kcal/mol is calculated for the motion of DNA.