Figure 3.

Tail-train-loop configurations of a chromatin polymer pinned at one or both ends to a neutral surface NP. This experiment models the conformations of a chromatin polymer anchored at one or both ends to a nuclear lamina devoid of attraction strength, at the end of simulations. (a) Percentage of structures with a tail (gray), train (red) and loop (blue) configuration as a function of bead position along the chain (x axis), with one anchor to NP (bead 1). Increasing color intensity depicts increasing polymer stiffness L_P (legend). Train configurations being insensitive to L_P, the red symbols appear superimposed. Lines are shown for data points at L_P = 5 nm (modeling a flexible chromatin chain) for easier visualization of the trends. (b,c) Percentage of one-anchor point structures with (b) the indicated number of tails, trains and loops (x axis) and (c) the indicated number of beads in each of these tail (gray), train (red) and loop (blue) configurations. (d) Percentage of structures with a tail, train, loop configuration for a polymer pinned at both ends to NP (bead 1, 12), as a function of polymer stiffness L_P (color intensity; legend). Data are shown separately for two Euclidian distances along NP: (i) d_E = 50 nm (relaxed chain) and (ii) d_E = 300 nm (stretched chain). Data for other d_E values are shown in Figure S1b. Lines connect data points for L_P = 5 nm (flexible chain) for clearer visualization of the trends. (e,f) Percentage of two-anchor point structures with (e) the indicated number of configuration and (e) the indicated number of beads in each configuration as in (b) and (c); shown for two examples of L_P (a flexible chain with L_P = 5 nm and a semi-flexible chain with L_P = 50 nm), and two d_E conditions (a relaxed chain with d_E = 50 nm and a stretched chain with d_E = 300 nm). Impact of polymer flexibility dominates over polymer stretching on its configurations at NP. We infer that chromatin stiffness influences contacts with the lamina to a greater extent than how stretched the chromatin domain is: greater flexibility, such as in euchromatin relative to heterochromatin, favors multiple interaction configurations at the lamina