Hydrodynamic studies of a DNA-protein complex. Dimensions of the complex of single-stranded 145 base DNA with gene 32 protein of phage T4 deduced from quasi-elastic light scattering.

The translational diffusion coefficient of the saturated complex of single-stranded 145 base DNA and the helix-destabilizing protein of phage T4, GP32, can be measured at equilibrium by means of quasi-elastic light scattering. If the complex is considered as a rigid rod one can estimate its dimensions by combining the translational diffusion coefficient with earlier data on rotational diffusion. It was found that the average base-base distance of the 145 base DNA in the complex is between 4.3 and 4.7 A, while the diameter of the complex is between 44 and 68 A. This suggests that the conformation of the complex must be such that a large amount of water is trapped.