Binding of DNA-bending non-histone proteins destabilizes regular 30-nm chromatin structure - Fig 1

<p>(a) When the DNA (yellow chain) is wrapped around the histone octamer (blue), we can represent the direction of the DNA segments that enters and exits the histone core as two vectors as shown here. The relative orientations of these entry/exit vectors will influence the local structure of the chromatin. (b) Linker DNA is typically rigid and straight. Rigid linker DNA and restricted orientations of entry/exit DNA segments will promote a zig-zag structure. (c–d): Schematic diagram describing the models: (c) Bead-spring model—DNA is modelled as a polymer made of beads of type-1 (yellow). 14 DNA-beads wrap around the histone-octamer bead (type-2, blue) to form a nucleosome. The picture also depicts linker histone H1 constraining entry/exit DNA beads (black spring), non-histone protein bending the linker region (red spring), and rigid linker regions when it is free of non-histone proteins. (d) Equivalently, nucleosome is considered as a bead that constraints the entry/exit DNA segments at an angle <i>α</i>_<i>n</i>. (e) FRC model—chromatin is modelled as a long 3D chain of <i>N</i> vectors. Yellow vectors represent linker DNA segments, which make a small angle <i>θ</i>_<i>d</i> with respect to its neighbor vector (in the absence of a non-histone protein); blue arrows represent histone-bound DNA having an angle <i>θ</i>_<i>n</i> = <i>π</i> − <i>α</i>_<i>n</i> between them. When a non-histone protein is present in the linker region, yellow tangents make a relative angle of <i>θ</i>_<i>p</i> as shown.