title: High-salt d(CpGpCpG), a left-handed Z' DNA double helix.
abstract: The DNA tetramer d(CpGpCpG) or CGCG crystallizes from high-salt solution as a left-handed double helix, the Z' helix. Its structure differs from that of the other known left-handed helix, Z-DNA, by a Cl'-exo sugar pucker at deoxyguanosines rather than C3'-endo, and these represent two alternative solutions to the same steric constraint arising from the syn glycosyl bond orientation. The apparent molecular basis for the Z to Z' transition in going from intermediate to high salt is substitution of a bound anion for water at guanine amino groups, and consequent charge repulsion of anions and backbone phosphates.
mesh_terms: D000438:Alcohols; D001483:Base Sequence; D001665:Binding Sites; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004247:DNA; D007477:Ions; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides; D012492:Salts; D014867:Water
chemical_list: D000438:Alcohols; D007477:Ions; D009838:Oligodeoxyribonucleotides; D012492:Salts; D014867:Water; D004247:DNA