Structure of the B DNA cationic shell as revealed by an X-ray diffraction study of CsDNA. Sequence-specific cationic stabilization of B form DNA.

Synchrotron radiation diffraction data for phage T2 CsDNA fibres have been used to determine the co-ordinates of the caesium ions in crystalline B form DNA. The R value is 0.16 for an optimized structure.

[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.

An x-ray diffraction study of ribosome structure.

Dense gels of E. coli 70 S ribosomes, their 50 S subunits, CM-like particles, RNP strands and their fragments, 38 S particles obtained from RNP strand folding upon addition of Mg2+ ions, and of unoriented salt-free and free rRNA sodium and magnesium salts were studied by X-ray diffraction. It was shown that under dense gel conditions RNA molecules contained in ribosomes unfolded by desalting, like all other particles considered here, have helical regions.