  The probability distributions for bending angles in double helical DNA
obtained in all-atom molecular dynamics simulations are compared with
theoretical predictions. The computed distributions remarkably agree with the
worm-like chain theory for double helices of one helical turn and longer, and
qualitatively differ from predictions of the semi-elastic chain model. The
computed data exhibit only small anomalies in the apparent flexibility of short
DNA and cannot account for the recently reported AFM data (Wiggins et al,
Nature nanotechnology 1, 137 (2006)). It is possible that the current atomistic
DNA models miss some essential mechanisms of DNA bending on intermediate length
scales. Analysis of bent DNA structures reveals, however, that the bending
motion is structurally heterogeneous and directionally anisotropic on the
intermediate length scales where the experimental anomalies were detected.
These effects are essential for interpretation of the experimental data and
they also can be responsible for the apparent discrepancy.
