X-ray scattering evidence that calf thymus DNA in solution is a double helix and not a warped zipper.

: Isotropic X-ray scattering experiments with calf thymus DNA in solution under B-form conditions were used to differentiate between the double helical and the side by side structure models. By comparison of experimental and theoretical scattering curves calculated from the atomic coordinates of the molecule models, two sterically refined SBS models can be excluded for calf thymus DNA. The structural basis of the differences between the experimental scattering curves and the theoretical curves for the double helix on the one hand and for the two SBS models on the other, is interpreted using high resolution electron distance distribution functions of the models.