Figure 5.
Tail-train-loop configurations at a surface NP fitted with varying attraction potentials. This experiment determines the conformations of a chromatin chain (tail, trains and loops) anchored at one or both ends to the lamina which here is fitted with a variable attraction potential (εads). A strong potential (εads = 1; top graphs) stably attracts the whole chain to the surface, while a very weak potential (εads = 0.005; bottom graphs) exerts a minimal, if any, effect. (a) Percentage of beads in tail-train-loop configurations (legend) in simulations with one anchor point, as a function of bead position along the chain (x axis), attraction potential (εads = 0.005–1) and chain stiffness LP (legend). (b) Same as in (a) for a polymer with two anchor points and as a function of dE; (i) dE = 50 nm; (ii) dE = 300 nm. Lines connect data points for LP = 5 nm for clearer visualization of the trends (tail, train, loop). The data demonstrate the requirement for an attraction potential to generate long-lasting interactions with NP, and that these involve cooperative recruitment of neighboring beads. Propensity for cooperative recruitment is exacerbated by polymer stiffness and stretching. Implications are that, at the genomic scale examined here, recruitment of chromatin to the nuclear lamina invokes extensions of existing LADs (or of lamina-bound sites within LADs). This recruitment is enhanced for heterochromatic domains such as those found in bona fide LADs