Analysis of low angle light scattering results from T7 DNA

Selected light scattering data, obtained in earlier studies on T7 DNA in 0.195 M Na+, are analyzed by comparison with calculations from the theory of wormlike coils, both with and without excluded volume effects. The results confirm the conclusion from an earlier criticism, that linear extrapolations of data from the 10 degrees to 20 degrees angular range give incorrect values for the limiting molecular weight, MT, and for the limiting root-mean-square radius, RT. Further, it is shown that the excluded volume parameter, epsilon, must be used to provide a proper fit of calculated curves to experimental data. The revised analysis gives the following parameters for T7 DNA:MT = 25.5 X 10(6); RT = 587 nm; epsilon = 0.08; and the statistical segment length, 1/lambda' = 120 nm. These parameters agree well with other values in the literature. The method of analysis, therefore, provides reliable results from light scattering data on high-molecular-weight, native DNA.