Ultrasonic Scission of Deoxyribonucleic Acid in Aqueous Solution II. Precipitational Fractionation and Molecular Weights of Sonicated Samples

Abstract

Four sonicated calf thymus deoxyribonucleic acid (DNA).samples irradiated at different energies, whose molecular weights Mw were 5.7×105, 3.4×105, 2.4×105, and 2.4×105, respectively, as described in the preceding paper, were fractionated in 0.2 M NaCl aqueous solutions by the successive precipitation method with acetone as the precipitant. Each sample was separated into four fractions, each of which was dissolved in 1 mM NaCl and freeze-dried for storage. The molecular weight and molecular weight distribution were determined by means of intrinsic viscosity (25°C), GPC (20°C), and gel electrophoresis (0°C), and compared with those of unfractionated samples. The molecular weight of each fractionated DNA sample was found to be in the range between 0.7×105 and 7×105, while the degree of polydispersity in terms of Mw/Mn was found to be between 1.06 and 1.77, any of which is narrower than the values of the corresponding unfractionated sample. The hyperchromicity of each fractionated sample was estimated from the melting curve. It was always larger than 34%, which indicates that the double-stranded helical structure was maintained in the process of fractionation.