{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"702db1102bf43fa654684ea4cf84486af54c3c6dee3f016208bf7d4ae935ca7c","created":"2026-10-03T07:17:57Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"ae7960b72f5c64bc0b963178506a4f932d4baf04081ca9c83a00ba969bef392f","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"bio.chromatin-extrusion.motor-mechanism","kind":"well-posed","literature_status":"partially-resolved","n":"1","parents":[],"plain":"Cohesin and condensin are ring-shaped protein machines that pull DNA into loops by burning ATP. Single-molecule experiments show steps of hundreds of base pairs, comparable to the size of the protein, and how the structure achieves this is unknown.","posed_since":"","precise":"Determine the conformational cycle of cohesin or condensin that couples ATP binding and hydrolysis to DNA translocation, explaining the measured step-size distribution (of order hundreds of base pairs per step, approximate), the force-velocity relation with stall at DNA tensions of order $10^{-8}\\text{ to }10^{-7}\\,\\mathrm{dyn}$ depending on the complex (approximate), and one-sided versus two-sided extrusion. Answer: a structural-kinetic model that reproduces these measurements.","problem_ref":null,"references":"","settled_by":"Time-resolved structures or single-molecule FRET of the motor cycle combined with force spectroscopy that match one model's predicted step and force-velocity statistics.","status_note":"Cryo-EM structures constrain the cycle, but several competing translocation models remain in 2026, to this survey's knowledge.","title":"Stepping mechanism of SMC loop-extruding 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