title: Mechanism of copper mediated triple helix formation at neutral pH in Drosophila satellite repeats.
abstract: The highly repeated Drosophila melanogaster AAGAGAG satellite sequence is present at each chromosome centromere of the fly. We demonstrate here how, under nearly physiological pH conditions, these sequences can form a pyrimidine triple helix containing T.A-T and CCu.G-C base triplets, stabilized by Cu2+ metal ions in amounts mirroring in vivo concentrations. Ultraviolet experiments were used to monitor the triple helix formation at pH 7.2 in presence of Cu2+ ions. Triplex melting is observed at 23 degrees C. Furthermore, a characteristic signature of triple helix formation was obtained by Fourier transform infrared spectroscopy. The stabilization of the C.G-C base triplets at pH 7.2 is shown to occur via interactions of Cu2+ ions on the third strand cytosine N3 atom and on the guanine N7 atom of the polypurine target strand forming CCu.G-C triplets. Under the same neutral pH conditions in absence of Cu2+ ions, the triple helix fails to form. Possible biological implications are discussed.
authors.affiliation: Laboratoire de Biophysique Moléculaire, Cellulaire et Tissulaire (BioMoCeTi), Unité Mixte de Recherche, Centre National de la Recherche Scientifique 7033, Université Paris 13, 93017 Bobigny cedex, France.
authors.forename: C
authors.initials: C
authors.lastname: Paris
authors.forename: F
authors.initials: F
authors.lastname: Geinguenaud
authors.forename: C
authors.initials: C
authors.lastname: Gouyette
authors.forename: J
authors.initials: J
authors.lastname: Liquier
authors.forename: J
authors.initials: J
authors.lastname: Lacoste
mesh_terms: D000818:Animals; D003198:Computer Simulation; D003300:Copper / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D004276:DNA, Satellite / Q000737:chemistry*; D004331:Drosophila melanogaster / Q000737:chemistry / Q000235:genetics*; D006863:Hydrogen-Ion Concentration; D018895:Microsatellite Repeats; D008956:Models, Chemical; D008958:Models, Molecular; D009690:Nucleic Acid Conformation
chemical_list: D004276:DNA, Satellite; C051802:triplex DNA; D003300:Copper; D004247:DNA