Figure 5.

Summary of coarse-grained computer simulations of the 12–177 nucleosome array with added Mg²⁺. Data obtained for three different models of the array mimicking the WT, Quad or tailless array are shown as indicated in the (b) graph legend. Data calculated for an array with a single charge quenched in the histone H4 tail mimicking a single modification are not displayed since they are very close to the data of the WT array. Representative snapshots in (a) show folding of the Quad (left) and WT (right) arrays at bulk Mg²⁺ concentration 2.7 mM, demonstrating the moderate effect on folding caused by quenching the four charges K5,8,12,16 of the histone H4 tail. Dependencies of radius of gyration, R_g, (b); sedimentation velocity coefficient, s_20,w, (c); and intensity of the maximum in the external tail—central core particle RDF (d) on bulk concentration of Mg²⁺. The external tail-core RDF signals the propensity of tail bridging to neighboring nucleosomes. Bulk concentration of Mg²⁺ is defined as concentration of Mg²⁺ ions averaged over the regions of simulation cell with low electric filed from the nucleosome array (32).