title: "Alternating B-DNA" conformation for the oligo(dG-dC) duplex in high-salt solution.
abstract: The high resolution 1H and 31P NMR spectra of the (dG-dC)8 duplex have been recorded in low- and high-salt solutions in order to evaluate the structural aspects of the salt-induced transition of oligo(dG-dC) in solution  [Pohl, F. M. & Jovin, T. M. (1972) J. Mol. Biol. 67, 375-396]. The NMR data require that the (dG-dC)8 duplex in 4 M NaCl adopt an "alternating B-DNA" conformation for which the symmetry unit repeats every two base pairs. By contrast, the oligomer duplex in low-salt solution is of the regular B-DNA type in solution. The chemical shift parameters for oligo(dG-dC) in high-salt solution demonstrate that every other glycosidic torsion angle and phosphodiester linkage adopts a different conformation from that observed in regular B-DNA. We demonstrate further that the generation of the "alternating B-DNA" structure is facilitated by introduction of halogen atoms at the 5 position of pyrimidine and that this probably reflects the greater overlap of this position with adjacent base pairs in high salt solution. An "alternating B-DNA" model has recently been proposed for alternating deoxy purine-deoxy pyrimidine polynucleotides based on the x-ray structure of pdA-dT-dA-dT [Klug, A., Jack, A., Viswamitra, M.A., Kennard, O., Shakked, Z. & Steitz, T.A. (1979) J. Mol. Biol., in press].
mesh_terms: D004247:DNA; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides; D009841:Oligonucleotides; D009994:Osmolar Concentration; D012965:Sodium Chloride; D013696:Temperature
chemical_list: D009838:Oligodeoxyribonucleotides; D009841:Oligonucleotides; D012965:Sodium Chloride; D004247:DNA