Elastic origin of chiral selection in DNA wrapping

We investigated the mechanism that underlies the chiral selection on the direction of wrapping of DNA around a nucleosome core particle. A coarse-grained model for the formation of a nucleosome is introduced, in which DNA is treated as a semiflexible polymer and the histone core is modeled by a spherical particle. Asymmetric coupling between bending and twisting is incorporated into the model DNA, which is expected from the double-stranded helical structure of DNA. We show that the tendency of DNA to twist in a left-handed manner upon bending gives rise to the selective left-handed wrapping, provided that the size of the core particle is chosen appropriately. This result suggests the critical importance of the chiral asymmetry inherent in the bending-twisting elasticity of DNA as well as the size of the core in determining the handedness of wrapping in nucleosome formation.