A condensin protein complex creates a loop in DNA.

A protein complex called condensin (yellow, red and blue structure) tugs DNA into a loop in this artist’s rendering. Credit: Cees Dekker Lab TU Delft/Scixel

Molecular biology

The secrets of DNA loops revealed on camera

A protein complex swiftly reels a length of DNA into a loop.

Long strands of genetic material are packaged into cells with help from a molecule that pulls DNA into loops.

The protein complex condensin plays a key role in organizing DNA’s 3D structure, but researchers have disagreed on how the complex works. Now, Christian Haering at the European Molecular Biology Laboratory in Heidelberg, Germany, Cees Dekker at the Delft University of Technology in the Netherlands and their colleagues have captured real-time video of condensin in action for the first time. To do so, the team tethered both ends of a piece of DNA to a surface and marked it with fluorescent dye.

The condensin molecule anchored itself to the DNA and then started reeling the DNA strand towards the anchor point, forming a loop. The loop grew at an average rate of 600 base pairs — the building blocks of DNA — per second.