Sequence-dependent DNA curvature and flexibility from scanning force microscopy images

This paper reports a study of the sequence-dependent DNA curvature and flexibility based on scanning force microscopy (SFM) images. We used a palindromic dimer of a 1878-bp pBR322 fragment and collected a large pool of SFM images. The curvature of each imaged chain was measured in modulus and direction. It was found that the ensemble curvature modulus does not allow the separation of static and dynamic contributions to the curvature, whereas the curvature, when its direction in the two dimensions is taken into account, permits the direct separation of the intrinsic curvature contributions static and dynamic contributions. The palindromic symmetry also acted as an internal gauge of the validity of the SFM images statistical analysis. DNA static curvature resulted in good agreement with the predicted sequence-dependent intrinsic curvature. Furthermore, DNA sequence-dependent flexibility was found to correlate with the occurrence of A·T-rich dinucleotide steps along the chain and, in general, with the normalized basepair stacking energy distribution.