Fractionation of calf thymus deoxyribonucleic acid by density-gradient centrifugation

1. 1. Several samples of calf-thymus DNA were fractionated by ultracentrifugation in a CsCl density gradient. The buoyant densities and the absorbancy-temperature curves of the different fractions were determined. 2. 2. The fraction corresponding to the satellite band of calf-thymus DNA presented densities ranging from 1.711 g per cm3 to 1.713 g per cm3 and Tm (melting temperature) ranging from 90 to 94° in the different experiments. The same fraction, after heating and rapidly cooling, presented an absorbancy-temperature curve unusual for DNA of mammalian origin and similar to that obtained with bacterial DNA. 3. 3. A discrete DNA fraction with a density of 1.718-1.719 g per cm3 was constantly detected in all the preparations.