Fig. 1. The model phase transition from a coil to a globule phase separated state.
a Cartoon of the Strings and Binders (SBS) polymer model of chromatin showing the specific binding sites along the chain (top) and a 3D conformation of the system folded by the action of cognate binders (bottom). b The SBS model of the studied chr21:34.6-37.1 Mb locus in human HCT116 cells has four types of binding sites, forming four binding domains each represented with a different color. Their genomic location and abundance are shown. A cartoon is sketched (bottom) of the model polymer chain and the color scheme used in the 3D representations in c). c Upon increasing the binder concentration, the model has a phase transition from a coil to a globule phase separated state, a more condensed structure made of partially separated globules, as signaled by a sharp decrease of the system order parameters, respectively the equilibrium gyration radius Rg (top) and average separation score (bottom). d The intrinsic degeneracy of the globule phase separated state, enhanced by the overlapping genomic organization of the binding domains, corresponds to a variety of 3D conformations: two structures are shown where, for example, the green binding domain collapses respectively onto the brown and the blue domain.