Small-angle scattering of chain molecules in a hydrodynamic field. The internal rigidity of double-stranded DNA

Small-angle X-ray scattering data from flowing solutions of double-stranded calf thymus DNA, in phosphate buffer of pH 6.91 and 0.2 mol dm^-3 ionic strength, have been recorded over a velocity-gradient range from zero up to a maximum value of 15300 s^-1. In comparison with small-angle X-ray measurements performed on stationary solutions, the method of flowing the solution through a capillary tube provides information regarding the internal flexibility of the macromolecule in solution. All the X-ray data recorded in this work can be explained by a slightly modified bead-spring chain model of DNA, which consists of linear segments filled with touching beads. The segments are joined together at the ends to form a long array with complete flexibility at each joint. The lengths of the segments follow a Gaussian distribution with a root-mean-square length equal to 100 nm. The diameter of each bead is equal to 3.0 nm.