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Doing A Spin With DNA

April 17, 2005
Netherlands Organization For Scientific Research
A Dutch led international team of researchers has unravelled how nature releases the torque built up in DNA at the molecular level. The researchers from Delft University of Technology, the Ecole Normale Supérieure in Paris and the Sloan-Kettering institute in New York published their findings in the 31 March 2005 issue of Nature.
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A topoisomerase IB enzyme clamps onto a DNA molecule. The enzyme cuts through one of the two strands after which the DNA molecule can spin around in a cavity of the enzyme. (Illustration TUDelft/Tremani)

DNA consists of two long strands joined together by pairs of bases. Both strands wind around each other in the form of a double helix with the base pairs acting as the 'stairs' in a staircase. The sequence of these base pairs stores genetic information. During cell division genetic material is copied and the enzymes responsible for this must be able to transcribe the base sequences. This is only possible if the portion of DNA to be transcribed is unwound. This winding and unwinding of the DNA gives rise to torsional forces in the DNA, the magnitude of which increases as cell division progresses. These forces can delay the process of cell division and under certain conditions even stop it. Topoisomerase IB can reduce these torsional forces.

The enzyme releases the torsion from the DNA as follows: The enzyme surrounds the double-stranded DNA like a clamp and then temporarily cuts through one of the two DNA strands. The accumulated torsional forces in the DNA are then spun out around the intact strand. After a number of turns the topoisomerase ones again firmly grabs the spinning DNA and 'glues' (ligates) the broken stands neatly back together again. The researchers were able to determine the exact number of turns removed by the topisomerase between 'cutting' and 'gluing'.

The precise mechanism of topoisomerase IB is also important for cancer research. Drugs which inhibit the functioning of topoisomerase IB are already in clinical use, but can possibly be improved using the knowledge from this study.

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The above story is based on materials provided by Netherlands Organization For Scientific Research. Note: Materials may be edited for content and length.

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Netherlands Organization For Scientific Research. "Doing A Spin With DNA." ScienceDaily. ScienceDaily, 17 April 2005. <>.
Netherlands Organization For Scientific Research. (2005, April 17). Doing A Spin With DNA. ScienceDaily. Retrieved April 26, 2015 from
Netherlands Organization For Scientific Research. "Doing A Spin With DNA." ScienceDaily. (accessed April 26, 2015).

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