%0 Journal Article %A C. A. Brackley %A J. Johnson %A D. Michieletto %A A. N. Morozov %A M. Nicodemi %A P. R. Cook %A D. Marenduzzo %T Non-equilibrium chromosome looping via molecular slip-links %D 2016 %R 10.1101/095992 %J bioRxiv %P 095992 %X We propose a model for the formation of chromatin loops based on the diffusive sliding of a DNA-bound factor which can dimerise to form a molecular slip-link. Our slip-links mimic the behaviour of cohesin-like molecules, which, along with the CTCF protein, stabilize loops which organize the genome. By combining 3D Brownian dynamics simulations and 1D exactly solvable non-equilibrium models, we show that diffusive sliding is sufficient to account for the strong bias in favour of convergent CTCF-mediated chromosome loops observed experimentally. Importantly, our model does not require any underlying, and energetically costly, motor activity of cohesin. We also find that the diffusive motion of multiple slip-links along chromatin may be rectified by an intriguing ratchet effect that arises if slip-links bind to the chromatin at a preferred "loading site". This emergent collective behaviour is driven by a 1D osmotic pressure which is set up near the loading point, and favours the extrusion of loops which are much larger than the ones formed by single slip-links. %U https://www.biorxiv.org/content/biorxiv/early/2016/12/21/095992.full.pdf