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How a cell keeps its 2 metres of DNA without knots? Methods of rope climbers may be in play

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Posted April 26, 2019

DNA strands are long and fussy. They can actually tie into knots, makings parts of them difficult to read. And yet about 2 metres of DNA can be neatly packaged in each of our cells without much problem. How? Scientists from the Universities of Edinburgh and Padova in Italy studied the process on unravelling knotted strands of DNA and it is a bit like untying climbing ropes.

DNA has to stay without tangles and knots for it to be easily readable. Image credit: Irina Gelbukh via Wikimedia (CC BY-SA 3.0)

DNA is so small it is difficult to see even with our current technology. However, it is also very long – each cell contains approximately 2 metres of DNA. If you can imagine how small a cell is, you will understand that DNA strands can easily become knotted and difficult to read. Scientists studied the process of untying these knots by creating computer models of DNA with knots and links. This helped identifying two sets of proteins in cells that work together to keep the strands unknotted. These proteins help avoiding tangles that would have tremendous negative consequences.

One of the proteins involved is from SMC family. It reminded scientists of a belay device used by rock climbers. Belay device passes ropes through a series of loops, guiding it and essentially preventing tangles. Another set of proteins, called TopoII, was already thought of being responsible for preventing tangles, but its role hasn’t been described until now. Both of these proteins are found in many organisms. Scientists think that their role of keeping strands of DNA organized could be observed throughout nature. And it makes sense. Since DNA is seen across pretty much all species and it is often long and complicated, it needs to be managed to avoid hampering biological processes.

And so SMC works like a belay device – it slides back and forth to enlarge or reduce loops in linked segments of DNA. In this way SMC squeezes and compresses knots, which can then be recognized by the TopoII protein, which then proceeds to untangle the mess. Scientists say that this explains how such a long DNA chain can be organized in a cell so neatly. Dr Davide Michieletto, one of the authors of the study, said: “DNA’s long strands might be expected to become horribly tangled – a bit like pulling knotted headphones out of your pocket. But instead, nature has created these amazing machines to address this problem in a remarkable way, seemingly across many species”.

We still don’t know a lot about how our DNA functions and is organized in our cells. Cells are extremely small and contain various different components alongside DNA. It is interesting how scientists recognized rope climbing methods in the tiny work of a couple of proteins. Hopefully, this knowledge will encourage looking even deeper into organization of DNA strands and eventually we will find ways of repairing damaged DNA.

 

Source: University of Edinburgh

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