Fig. 10.

Conformation of legs produced by active loop extrusion. (A) Schematic of legs, each with genomic length $g_{\mathit{leg}}\left(t\right)\sim {\left(v_{\mathit{ex}}t\right)}^{1/D}$ and mean square size $<r_{\mathit{leg}}^2\left(t\right)<\sim {\left(v_{\mathit{ex}}t\right)}^{2/D}$. The left-hand schematic shows the initial chromatin conformation with fractal dimension $D$ at the time of cohesin binding. The right-hand schematic shows leg extension at time t. (B) Mean square distance between cohesin and a locus $s_{c,out}$ away outside of its extruded loop at different times after binding (solid lines) compared to $<r_0^2\left(s_{c,out}+v_{\mathit{ex}}t\right)<$, the unperturbed mean squared sizes of sections with genomic lengths $s_{c,out}+v_{\mathit{ex}}t$ (dashed lines), from hybrid MD—MC simulations of single cohesins actively extruding a relaxed polymer chain ($D\approx 2$) with $v_{\mathit{ex}}\approx 0.3$ kbp per ${\tau }_0$ ($\kappa \approx 0.15$). The solid black line is the predicted limiting behavior for full polymer extension. The solid green curve is the unperturbed mean square sizes of sections with genomic length $s_{c,out}$. The dashed green line is the predicted scaling behavior of these unperturbed sizes without extrusion.