Dynamic barriers lead to distinct regimes for predicted loop size. (A) Heat map showing loop sizes as a function of bound (τb) and unbound (τu) times for simulations with a simplified layout of two convergent barriers, as illustrated in B. The red dashed line indicates loop size = 87.5 kb, equivalent to the spacing between barriers (δ). Dashed lines indicate constant barrier occupancies between 0.1 and 0.9, spaced by 0.1. (B) Illustration of simplified convergent barrier layout and three regimes of extruder lifetime compared to barrier bound times. Red arrows indicate movement of the extruder. At short extruder lifetimes, (i) the extruder has yet to encounter the barrier and moves unimpeded; at intermediate lifetimes, (ii) the extruder becomes stalled if the barrier is occupied, yet proceeds unimpeded if the barrier is unoccupied; at long lifetimes, (iii) the extruder can bypass the barrier position by continued loop enlargement after stalling (right), or simply continue unimpeded if the barrier was unoccupied. (C) As in A, but for the analytical formula for loop size as a function of bound and unbound times. (D) Loop size versus occupancy for analytical predictions (lines) versus simulations (dots). Note how curves approach the “static” barrier model at large τb (darker lines), where loop size is a linearly decreasing function of the occupancy.
