DYNAMIC LIGHT-SCATTERING STUDY OF A MONODISPERSE-2311 BASE PAIR CIRCULAR DNA

Dynamic light scattering has been used to study the dynamics of a 2311bp (base pair) circular DNA at two different ionic strengths. The measured intensity autocorrelation functions at different scattering vector lengths were analyzed by the inverse Laplace transform program, CONTIN, to separate translational and internal motions. The translational diffusion coefficient of the chain is in good agreement with the predictions of the circular wormlike cylinder model developed by Fujii and Yamakawa with a persistence length of 45 nm for DNA at 0.2 M salt. The longest internal relaxation time slows down when decreasing the ionic strength to 0.01 M. It was concluded from this result that the relaxation time is not dominated by the local stiffness of the chain. The overall picture of the difference between the dynamics of linear and circular wormlike chains is well represented by the free-draining Rouse-Zimm model with included stiffness. A quantitative comparison, however, between dynamic form factors obtained experimentally with the predictions of different circular wormlike chain theories and the free-draining Rouse-Zimm model reveals substantial discrepancies between the experimental dynamic form factors and the models. Possible reasons are discussed.