Sequence-Disorder Effects on DNA Entropic Elasticity

DNA stretching experiments are usually interpreted using the wormlike chain model; the parameter A appearing in the model is then interpreted as giving the elastic bend stiffness of the double helix. Actually, however, the value of A obtained by this method is a combination of bend stiffness and intrinsic bend effects reflecting sequence information, just as at zero stretching force. This observation resolves the discrepancy between the value of A measured in these experiments and the larger “dynamic persistence length” measured by other means. On the other hand, the twist stiffness deduced from torsionally constrained stretching experiments suffers no such correction. The calculation is very simple and analytic; it explains the success of the naive wormlike chain model over the entire force range of DNA stretching experiments.