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J. Biol. Chem., Vol. 277, Issue 11, 8906-8911, March 15, 2002

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Interaction of Human Nuclear Topoisomerase I with Guanosine Quartet-forming and Guanosine-rich Single-stranded DNA and RNA Oligonucleotides^*

Christophe Marchand, Philippe Pourquier, Gary S. Laco, Naijie Jing^§, and Yves Pommier^¶

From the  Laboratory of Molecular Pharmacology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892-4255 and ^§ Section of Infectious Diseases, Department of Medicine, Baylor College of Medicine, Houston, Texas 77030

Human nuclear DNA topoisomerase I (top1) plays a crucial role in DNA replication, transcription, and chromosome condensation. In this study, we show that intra- and intermolecular guanosine quartets (G-quartets) can inhibit top1-mediated DNA cleavage at a high affinity site. Top1-mediated DNA cleavage was also inhibited by a 16-mer single-stranded oligodeoxynucleotide (ODN) containing a G-rich sequence (G₂T₂G₅TG₂TG₃) and by its RNA equivalent, neither of which form G-quartet structures. A comparison of various single-stranded ODN for their ability to inhibit top1-mediated DNA cleavage indicated that G-rich sequences containing repeats of 2 or 3 consecutive guanines interspaced with thymines specifically inhibited top1. We also found that both single-stranded and G-quartet-forming ODNs bind to top1 without being cleaved by the enzyme. These results demonstrate that either DNA or RNA G-rich single-stranded and G-quartet-forming oligonucleotides can bind to top1 and prevent cleavage of duplex DNA.

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