Proteins ‘work together' to keep DNA tangle-free

The process is similar to that used to control climbing ropes.

A process that cells use to unravel knotted strands of DNA – resembling a method used to control climbing ropes – has been uncovered by scientists.

Experts have identified two sets of proteins that work together to keep the strands unknotted, avoiding tangles that would hamper biological processes.

The breakthrough study is the first to explain how these two families keep DNA tangle-free under the confined, crowded conditions of the cell.

Dr Davide Michieletto, who led 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.”

The proteins are found in many organisms and scientists believe their role in managing DNA may be common throughout nature.

One family of proteins – known as SMC – acts like a belay device used by rock climbers, which passes ropes through a series of loops.

They have been found to work alongside another set, known as TopoII, which was previously thought to help solve tangles, but in a way not well understood.

Researchers at the Universities of Edinburgh and Padova in Italy studied the process by creating computer models of DNA with knots and links.

They found SMC acts like a belay, sliding back and forth to enlarge or reduce loops in linked segments of DNA.

Knots are first squeezed and compressed by SMC, and subsequently they are easily detected and resolved by TopoII.

The findings help explain how about 2 metres of DNA can be packaged in each of our cells, in a space about the width of a hair.

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