AI Article Synopsis
- Topoisomerase II is essential for managing the topology of double-stranded DNA by resolving issues like knots through DNA cleavage, though the regulation of this process is poorly understood.
- Single-molecule fluorescence experiments reveal a new sequence of events during DNA cleavage, including stages of binding to DNA, bending it in a sequence-specific manner, and random cleavage.
- The presence of Mg(2+) ions and the clamping action of the N-gate protein significantly enhance DNA bending and cleavage efficiency, indicating that accurate DNA cutting by topoisomerase II is tightly linked to how it bends the DNA.
Article Abstract
Topoisomerase II resolves intrinsic topological problems of double-stranded DNA. As part of its essential cellular functions, the enzyme generates DNA breaks, but the regulation of this potentially dangerous process is not well understood. Here we report single-molecule fluorescence experiments that reveal a previously uncharacterized sequence of events during DNA cleavage by topoisomerase II: nonspecific DNA binding, sequence-specific DNA bending, and stochastic cleavage of DNA. We have identified unexpected structural roles of Mg(2+) ions coordinated in the TOPRIM (topoisomerase-primase) domain in inducing cleavage-competent DNA bending. A break at one scissile bond dramatically stabilized DNA bending, explaining how two scission events in opposing strands can be coordinated to achieve a high probability of double-stranded cleavage. Clamping of the protein N-gate greatly enhanced the rate and degree of DNA bending, resulting in a significant stimulation of the DNA cleavage and opening reactions. Our data strongly suggest that the accurate cleavage of DNA by topoisomerase II is regulated through a tight coordination with DNA bending.
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| http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3286967 | PMC |
| http://dx.doi.org/10.1073/pnas.1115704109 | DOI Listing |
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