Speed and lifetime of loop extrusion inside living cells
In plain words
Purified cohesin extrudes DNA in a test tube at roughly a thousand base pairs per second. How fast it works inside a crowded nucleus, and how long loops last, has been measured at only a few sites.
Precise statement
Measure, genome-wide in living mammalian cells, the cohesin extrusion speed (kb/s), residence time on chromatin, and the fraction of time a CTCF-anchored loop is fully formed, and test whether polymer simulations with these parameters reproduce Hi-C contact maps (contact probability P(s) and domain boundaries) without refitting. Answer: values with uncertainties and the outcome of the consistency test.
What would settle it
Live-cell imaging of many loci, or time-resolved contact mapping after acute cohesin release, combined with parameter-free polymer simulation.
Status in the literature
Live imaging of one mouse locus (2022) found the fully looped state present only a few percent of the time; genome-wide in vivo rates remain open.