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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