Structure of the B DNA cationic shell as revealed by an X-ray diffraction study of CsDNA

摘要: Synchrotron radiation diffraction data for phage T2 CsDNA fibres have been used to determine the co-ordinates of caesium ions in crystalline B form DNA. The R value is 0·16 an optimized structure. are distributed equally between narrow and wide grooves DNA located close dyad axes lying planes adjacent base-pairs. On widegroove side cations separated from nearest phosphate atoms by a hydration layer one two water molecules thick. In groove directly co-ordinated base and, six out ten possible stacking types, chelation complexes: O-2(Pyr)-Cs + -O-2(Pyr), -N-3(Pur) or N-3(Pur)-Cs -N-3(Pur), which stabilize conformation. steric properties such complexes as estimated different sequences consistent with structural behaviour double-helical polynucleotides sequences, experimentally observed.