  Recent work indicates that twist-bend coupling plays an important role in DNA
micromechanics. Here we investigate its effect on bent DNA. We provide an
analytical solution of the minimum-energy shape of circular DNA, showing that
twist-bend coupling induces sinusoidal twist waves. This solution is in
excellent agreement with both coarse-grained simulations of minicircles and
nucleosomal DNA data, which is bent and wrapped around histone proteins in a
superhelical conformation. Our analysis shows that the observed twist
oscillation in nucleosomal DNA, so far attributed to the interaction with the
histone proteins, is an intrinsic feature of free bent DNA, and should be
observable in other protein-DNA complexes.
