B-DNAS CONFORMATIONAL SUBSTATES REVEALED BY FOURIER-TRANSFORM INFRARED DIFFERENCE SPECTROSCOPY

Conformational substates (CSs) of deoxyribonucleic acid (DNA), essenti al for its dynamics and function, are spectroscopically revealed by a new low-temperature method. Hydrated films of the sodium salt of DNA c ontaining up to approximate to 100% of the B-form were quenched into t he glassy metastable state at 77 K. Attainment of equilibrium in the g lass --> liquid transition region by interconversion of CSs was follow ed isothermally by Fourier transform infrared spectroscopy. Kinetic an alysis of difference spectra revealed two sequential relaxation proces ses and the spectral patterns of two distinct CSs of B-DNA, with expon ential interconversion kinetics for each vibrational mode. The charact eristic spectral features of the two CSs are also found in the spectru m of B-DNA in aqueous solution. The relevance of these CSs is discusse d with respect to the crystalline state and DNA-protein interaction.