1H nuclear magnetic resonance investigation of flexibility in DNA.

Abstract

Successful observations of proton NMR spectra of native double helical salmon sperm and calf thymus DNA of various lengths are reported. Measurements of the linewidths arising from proton-proton dipolar interactions are used to obtain information about the dynamic behavior of DNA helices in solution. Depending on which protons are used to monitor the local internal motions of the DNA, different results are obtained. The low-field resonances from H-bonded imino protons in the base pairs indicate that the correlation time for reorientation of base pairs is less than 3 .times. 10-7 s, whereas correlation times for motion of neighboring sugar protons relative to the aromatic protons are < 5 .times. 10-8 s for DNA that is over 200 base pairs long. There is probably more internal flexibility in the DNA molecules, especially in the backbone, than is indicated by classic hydrodynamic studies of DNA.