It is one of the great mysteries in biology: How does a cell neatly distribute its replicated DNA between two daughter cells? For more than a century, we have known that DNA in the cell is comparable to a plate of spaghetti—a jumble of intermingled strands. When cells divide, they have to pack two metres of DNA into tidy little packages—chromosomes. This packing is induced by proteins called condensin, but scientists are split regarding the actual mechanism. One argument holds that the protein works like a hook, randomly grasping somewhere in the jumble of DNA and tying it all together. Another holds that the ring-shaped protein pulls the DNA inward to create a loop. In a new study reported in Science, researchers from TU Delft, Heidelberg and Columbia University give the oop-extrusion argument a significant boost, demonstrating that condensin does, indeed, have the putative motor function required for this dynamic.