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Remarkably, living cells are able to package a jumble of DNA over two meters in length into tidy, tiny chromosomes while preparing for cell division. However, scientists have been puzzled for decades about how the process works. Researchers from the Kavli Institute of Delft University and EMBL Heidelberghave now isolated and filmed the process, and witnessed in real time how a single protein complex called condensin reels in DNA to extrude a loop. By extruding many such loops in long strands of DNA, a cell effectively compacts its genome so it can be distributed evenly to its two daughter cells. The scientists published their findings in Science.
This discovery resolves a heated debate in the field, as it finally answers a question that has been discussed in biology for over a century: Before dividing in two, DNA in a cell is comparable with spaghetti – a messy mixture of intermingled strands. The cell needs to organise this jumble in chromosomes to be able to divide its DNA neatly over both daughter cells. For many years, it has been clear that the protein complex condensin plays a key role, but until now, biologists were divided on exactly how. One theory held that condensin works like a hook that can grasp and connect DNA within the jumble of DNA, thus tying it together. Another theory suggested that the ring-shaped condensin pulls the DNA inwards to create a loop.
Cover - Article - Science - November - Scientists
In a cover article in Science last November, scientists from Delft and collaborating labs showed that condensin has the motor function needed for such loop extrusion. This added an important new piece to the puzzle, but as Kim Nasmyth from Oxford University noted in the accompanying perspective, "The discovery that condensin is a DNA translocase is certainly consistent with the idea that it functions as...
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