title: Strand orientation in the DNA quadruplex formed from the Oxytricha telomere repeat oligonucleotide d(G4T4G4) in solution.
abstract: The structure formed from the DNA oligonucleotide d(G4T4G4) (Oxy-1.5), which contains the Oxytricha telomere repeat T4G4, has been investigated by two-dimensional 1H and 31P NMR spectroscopy. Sequence-specific assignments have been obtained for the 1H and 31P resonances, using a combination of methods including comparisons to the inosine- and uracil-containing derivatives d(G4T4G3I) and d(G4UT3G4). The oligonucleotide forms a symmetrical bimolecular G-quadruplex with four G-quartets and thymine loops at opposite ends of the G-quartets. Guanines are alternatively syn and anti along each "strand" and all of the thymines are anti. The thymines loop diagonally across the G-quartet, resulting in a structure in which adjacent strands are alternately parallel and antiparallel and the glycosidic torsion angles are syn-syn-anti-anti around each G-quartet. There are three different types of grooves, a wide, a narrow, and two medium grooves. A diagonally looped quadruplex is formed in the presence of both Na+ and K+ counterions. The model structure of Oxy-1.5 is compared to the recently published crystal structure of Oxy-1.5 (Kang et al., 1992), which contains many of the same features as those found in solution but differs in that the thymines loop across an edge of the G-quartet.
authors.affiliation: Department of Chemistry, University of California, Los Angeles 90024.
authors.forename: F W
authors.initials: FW
authors.lastname: Smith
authors.forename: J
authors.initials: J
authors.lastname: Feigon
mesh_terms: D000818:Animals; D001483:Base Sequence; D016054:DNA, Protozoan / Q000737:chemistry*; D006859:Hydrogen; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008961:Models, Structural; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D016813:Oxytricha; D010758:Phosphorus; D012091:Repetitive Sequences, Nucleic Acid; D012996:Solutions; D016615:Telomere / Q000648:ultrastructure
chemical_list: D016054:DNA, Protozoan; D046911:Macromolecular Substances; D009838:Oligodeoxyribonucleotides; D012996:Solutions; D010758:Phosphorus; D006859:Hydrogen