DNA’s secret weapon against knots and tangles

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By Elie Dolgin

Leonid Mirny swivels in his office chair and grabs the power cord for his laptop. He practically bounces in his seat as he threads the cable through his fingers, creating a doughnut-sized loop. “It’s a dynamic process of motors constantly extruding loops!” says Mirny, a biophysicist here at the Massachusetts Institute of Technology in Cambridge.

Mirny’s excitement isn’t about keeping computer accessories orderly. Rather, he’s talking about a central organizing principle of the genome — how roughly 2 metres of DNA can be squeezed into nearly every cell of the human body without getting tangled up like last year’s Christmas lights.

He argues that DNA is constantly being slipped through ring-like motor proteins to make loops. This process, called loop extrusion, helps to keep local regions of DNA together, disentangling them from other parts of the genome and even giving shape and structure to the chromosomes.

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