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Biochemistry. 2004 Sep 7;43(35):11196-205.

Triple helix formation with Drosophila satellite repeats. Unexpected stabilization by copper ions.

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Laboratoire de Biologie Moléculaire et Cellulaire de la Différenciation, INSERM UR 309, Institut Albert Bonniot, Rond-point de la Chantourne, 38700 Grenoble, France.


The Drosophila melanogaster (AAGAGAG)(n) satellite repeat represents up to 1.5% of the entire fly genome and may adopt non-B DNA structures such as pyrimidine triple helices. UV melting and electrophoretic mobility shift assay experiments were used to monitor the stability of intermolecular triple helices as a function of size, pH, and backbone or base modification. Three to four repeats of the heptanucleotide motif were sufficient to allow the formation of a stable complex, especially when modified TFOs were used. Unexpectedly, low concentrations (40-100 microM) of Cu(2+) were found to favor strongly pyrimidine triplex formation under near-physiological conditions. In contrast, a much higher magnesium concentration was required to stabilize these triplexes significantly, suggesting that copper may be an essential stabilizing factor for pyrimidine triplexes.

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