Dynamic light-scattering studies on thermal motions of native DNAs in solution

The basic character of dynamic light-scattering properties of native DNA was investigated on two DNA samples. The degree of non-single exponentiality of photocount correlation functions, C(t), and its dependence on K are quantitatively characterized by two methods. The spectral linewidth, Ts, determined from C(t) exhibits a K dependence near to but significantly different from the prediction for Rouse-Zimm (RZ) chains by Dubois-Violette and De Gennes: It is inferred from data on lambda-DNA that the exponent in the K dependence of the spectral linewidth for native DNA takes a value larger than 3 in the K region corresponding to the 'K3' region for RZ chains. These results are in good agreement with the prediction from the dynamic theory of semiflexible chains presented by one of us (K.S.). The apparent diffusion coefficients are fairly insensitive to DNA concentration and ionic strength at large K. On the other hand, it is indicated that the stiffness of native DNA may vary with temperature even in a temperature range substantially lower than that of melting.