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Real-time imaging of DNA loop extrusion by condensin

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Science  22 Feb 2018:
eaar7831
DOI: 10.1126/science.aar7831

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Abstract

It has been hypothesized that Structural Maintenance of Chromosomes (SMC) protein complexes such as condensin and cohesin spatially organize chromosomes by extruding DNA into large loops. Here, we provide unambiguous evidence for loop extrusion by directly visualizing the formation and processive extension of DNA loops by yeast condensin in real-time. We find that a single condensin complex is able to extrude tens of kilobase pairs of DNA at a force-dependent speed of up to 1,500 base pairs per second, using the energy of ATP hydrolysis. Condensin-induced loop extrusion is strictly asymmetric, which demonstrates that condensin anchors onto DNA and reels it in from only one side. Active DNA loop extrusion by SMC complexes may provide the universal unifying principle for genome organization.

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