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1 August 2001 Strand Breaks in Whole Plasmid DNA Produced by the Decay of 125I in a Triplex-Forming Oligonucleotide
Irina V. Panyutin, Andrew N. Luu, Igor G. Panyutin, Ronald D. Neumann
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Abstract

Panyutin, I. V., Luu, A. N., Panyutin, I. G. and Neumann, R. D. Strand Breaks in Whole Plasmid DNA Produced by the Decay of 125I in a Triplex-Forming Oligonucleotide. Radiat. Res. 156, 158–166 (2001).

DNA strand breaks produced by the decay of 125I positioned against a specific site in plasmid DNA via a triplex-forming oligonucleotide were studied both in the immediate vicinity of the site of the decay with a single nucleotide resolution and in the whole plasmid by measuring the percentages of supercoiled, open-circular and linear forms. The localized breaks are distributed within 10 bp in each direction from the decay site with maxima in both strands just opposite the 125I-dC residue in the triplex-forming oligonucleotide. The distributions of breaks in the two DNA strands are almost symmetrical, in agreement with the geometry of the pyrimidine motif triplex. We found that about 25% of the double-strand breaks were located outside the 90-bp fragment containing the triplex-forming oligonucleotide binding sequence. The ratio of single- to double-strand breaks in the whole plasmid was 11 for bound triplex-forming oligonucleotide compared to 26 when the triplex-forming oligonucleotide was free in solution. The number of double-strand breaks per decay of 125I was 0.46 for bound triplex-forming oligonucleotide and 0.17 for free triplex-forming oligonucleotide. Comparing the data on the localized damage and those for the whole plasmid, we concluded that, in addition to DNA breaks that are confined to a helical turn around the 125I atom, the decay can produce breaks hundreds of base pairs away in the plasmid molecule. This linear plasmid molecule containing radiation-induced damage at a specific DNA site should be useful in studies of the molecular mechanisms of DNA repair.

Irina V. Panyutin, Andrew N. Luu, Igor G. Panyutin, and Ronald D. Neumann "Strand Breaks in Whole Plasmid DNA Produced by the Decay of 125I in a Triplex-Forming Oligonucleotide," Radiation Research 156(2), 158-166, (1 August 2001). https://doi.org/10.1667/0033-7587(2001)156[0158:SBIWPD]2.0.CO;2
Received: 6 December 2000; Accepted: 1 April 2001; Published: 1 August 2001
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