Correlated Local Bending of a DNA Double Helix and Its Effect on DNA Flexibility in the Sub-Persistence-Length Regime

Mechanical characteristics of DNA in the sub-persistence-length (l P ≈ 150 base pairs) regime are vital to many of its biological functions but not well understood. Recent experimental studies in this regime have shown a dramatic departure from the traditional worm-like chain model, which is designed for long DNA chains and predicts a constant flexibility at all length scales. Here, we report an improved model with explicit considerations of a new length scale l D ≈ 10 base pairs, over which DNA local bend angles are correlated. In this correlated worm-like chain model, a finite length correction term is analytically derived, and DNA flexibility is found to be contour-length-dependent. While our model reduces to the traditional worm-like chain model at length scales much larger than l P, it predicts that DNA becomes much more flexible at shorter sizes, in good agreement with recent cyclization measurements of short DNA fragments around 100 base pairs.