[Heavy cation position in the structure of the crystalline B-form of DNA]

Coordinates of caesium ions in DNA crystalline B-form were obtained by X-ray study of CsDNA with the use of synchrotron radiation. In conformity with the model that well meets the obtained set of structure factor amplitudes, the cations are located rather close to diad axes lying between the planes of successive nucleotide pairs. The cations in the narrow groove touch DNA surface, while those in the wide groove are rather far from the DNA molecule.