DNA spontaneously wrapping around a histone core prefers negative supercoiling: A Brownian dynamics study
Fig 6
Extension, twist and writhe changes of DNA during nucleosome-wrapping.
(A) The extension increment of the supercoiled DNA due to the nucleosome wrapping.Under tensional forces, the nucleosome wrapping increases the extension of the negatively supercoiled DNA while reducing the extension of the positively supercoiled DNA. (B) The mean extension increment resulting from nucleosome wrapping is a function of supercoil and stretching force. The positive increment in DNA extension due to nucleosome wrapping causes the decrease of the potential energy of the extended DNA, which is energetically favored. (C) Changes in the twist (ΔTw) and writhe (Wr) of the unconstrained DNA due to nucleosome-wrapping. (D)The changes in twist and writhe of (positive supercoils) DNA during winding around histone core. (Left) Extendedly (+) supercoiled DNA wraps around a histone under small force, e.g, f = 0 . 1pN. The induced + 1 linking number is mainly attributed to writhe, which causes work done during nucleosome wrapping. (Right) Highly tensional (+) supercoiled DNA wraps around a histone under large force, e.g, f = 10pN. The induced + 1 linking number is mainly attributed to twist, which increases twisting energy during nucleosome wrapping.