The basis for camptothecin enhancement of DNA breakage by eukaryotic topoisomerase I (original) (raw)

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Department of Microbiology, University of Washington

Seattle, WA 98195, USA

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Department of Microbiology, University of Washington

Seattle, WA 98195, USA

* To whom correspondence should be addressed

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Revision received:

26 September 1989

Accepted:

26 September 1989

Published:

11 November 1989

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Stephaie E. Porter, James J. Champoux, The basis for camptothecin enhancement of DNA breakage by eukaryotic topoisomerase I, Nucleic Acids Research, Volume 17, Issue 21, 11 November 1989, Pages 8521–8532, https://doi.org/10.1093/nar/17.21.8521
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Abstract

The eukaryotic topoisomerase I (topo I) is the target of the cytotoxic alkaloid camptothecin (CTT). In vitro , CTT enhances the breakage of DNA by topo I when the reaction is stopped with detergent. Although breakage at some sites is enhanced to a great extent while breakage at others is enhanced only minimally, CTT does not significantly change the breakage specificity of topo I in vitro . It has been suggested that CTT acts by slowing the reclosure step of the nicking-closing reaction. To test this hypothesis, we have measured the rate of reclosure for different break sites in the presence of CTT after adding 0.5 M NaCl to a standard low salt reaction. In support of the hypothesis, we find that topo I-mediated DNA breakage is enhanced the greatest at those sites where closure of the break is the slowest. These results suggest a mechanism for the toxicity of CTT in vivo .

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