Effect of Hydration and Metal Ions on DNA Conformations Studied by Vibrational Spectroscopy

Water molecules and metal ions play a fundamental role in the stabilization of nucleic acid structures. It has been extensively studied both theoretically (for review see Pullman et al. 1983) and experimentally by X-ray diffraction (for review see Rich et a). 1984, Dickerson 1987 ) and NMP. We would like here to give a few examples of how vibrational spectroscopy can be used to investigate the effect of water and ionic environment on DNA conformation. Local changes of DNA geometry may play a fundamental role in regulation of gene expression for example by modulating DNA-protein interactions, therefore the importance of the studies concerning the conformational variability of the DNA double helix. One of the advantages of vibrational spectroscopy is to allow one to obtain informations about nucleic acid helical geometries under a wide variety of physical states: solutions, gels, fibers, hydrated films, crystals. It is therefore possible to study the effect of hydration on the geometry of a DNA sequence and investigate the existence of possible conformational transitions. Vibratioal spectroscopy is thus able to establish a relationship between the results obtained in solid state by X-ray crystal diffraction and the structures determined in solution by NMR studies.