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BP: Fachverband Biologische Physik

BP 36: Statistical Physics of Biological Systems IV (joint session BP/DY)

BP 36.10: Vortrag

Freitag, 13. März 2026, 12:15–12:30, BAR/SCHÖ

Polymer theory shows DNA motors extrude loops in the monomeric mode — Kirill Polovnikov^{1, 2} and •Dmitry Starkov² — ¹Institute for Physics and Astronomy, University of Potsdam, Potsdam-Golm, Germany — ²Moscow, Russia

Cohesin-dependent loop extrusion is a key active mechanism of DNA organization, yet it remains unclear whether chromatin loops in living cells are generated primarily by individual cohesin motors or by higher-order structures. To fill this major gap, we build an analytical polymer-physics model that extracts a missing parameter - the linear density of loops - directly from Hi-C data. We focus on short genomic distances, where contact statistics simplify, resulting in a perturbative expression for the contact probability of a looped chain under a finite contact-detection radius. Our theory recapitulates a characteristic dip in the logarithmic derivative of the contact-probability that is broadly observed in experiments. By fitting this minimal model to a diverse range of mammalian Hi-C datasets, we infer approximately six loops per megabase. Independent imaging and mass spectrometry measurements of cohesin density are consistent with our inferred loop density, supporting the monomeric mode of DNA motors extrusion.

Keywords: chromatin; loop extrusion; cohesin; polymer physics; statistical physics