Sedimentation of DNA released from Chinese hamster cells

Under high pH and high salt conditions, Chinese hamster cells lyse and release a DNA-containing material of large molecular weight. With increasing lysis time, a smaller material is resolved from the large one. Relative to T4 DNA, the smaller is estimated to be approximately 2 x 10(8) daltons (number average). From a comparison of radiation data, the target size of the larger is about 15 times that of the smaller (probably a lower limit estimate). In addition to concentration of alkali, temperature, and time of lysis, the resolution of the smaller from the larger material is shown to be affected by other factors. Three of these are: fluorescent light exposure during lysis, X-irradiation before lysis, and incorporation of actinomycin D before lysis. All of these treatments result in degradation of the smaller molecules if large enough exposures are used. The sedimentation patterns of both DNA materials are strongly speed dependent. This probably results from changes in molecular conformation and concomitant increases in viscous drag with speed. The speed dependence differs qualitatively for the two materials, an observation which suggests that they differ in ways in addition to size.