Effect of Relative Centrifugal Force on the Apparent Size of DNA from Escherichia coli Cells

Abstract

Sedimentation coefficients were determined for the DNA from E. coli cells that had been lysed on top of alkaline sucrose gradients and some of the factors affecting the apparent size of the DNA were explored. Parallel experiments were carried out with the DNA from lysed T4 phage as a standard marker. The apparent size of single-stranded DNA from E. coli is strongly dependent on relative centrifugal force; regardless of the initial size, whether 50 or 140 S, all preparations sedimented at the same rate at high rotor speeds. The size of T4 phage DNA appeared to be too small to show an equally marked dependence of sedimentation coefficient on rotor speed under the conditions tested.Cells washed with EDTA solutions yielded DNA of a smaller size, while cells lysed on alkaline 25–40% sucrose gradients containing 1 M sodium ion yielded DNA with very high sedimentation coefficients.