Change of Conformation of DNA by Association with Proteins

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Abstract
A comparison of the conformation in solution of DNA‐protein associations with that of free DNA has been carried out for lysozyme, ribonuclease and bovine serum albumin. The solutions have been studied simultaneously by ultracentrifugation, light‐scattering, spectropolarimetry and viscometry.From the data it can be concluded: For DNA‐ribonuclease and DNA‐bovine serum albumin complexes, the interaction forces between complex particles themselves or between particles and solvent, decrease with increasing amounts of bound protein since the viscosity decreases markedly while there is only a small variation in the radius of gyration. For DNA‐lysozyme complexes, the slight increase in viscosity for low amounts of bound protein results from a simultaneous decrease of the interaction forces and a thickening of the filament. The molecular weight of DNA‐ribonuclease complexes increases as expected for a normal association. Those of DNA‐lysozyme complexes reveal at first a disaggregation of DNA under the influence of a low amount of protein, then with higher amounts of protein a normal increase in the molecular weight occurs up to the lysozyme concentration where aggregation sets in.In the case of DNA‐bovine serum albumin complexes, the apparent molecular weight of DNA decreases continuously with increasing amount of bound bovine serum albumin. The variation of the radius of gyration is dependent on the protein associated to DNA. In no case has a variation of secondary structure of the components been induced by their association.