Mechanism of copper mediated triple helix formation at neutral pH in Drosophila satellite repeats |
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Authors: | Paris C Geinguenaud F Gouyette C Liquier J Lacoste J |
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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. |
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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. |
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