Improved electrophoretic separation of supercoiled and relaxed DNA in the presence of ethidium bromide.

Supercoiled and relaxed DNA were resolved electrophoretically in the presence of 0.5 micrograms/ml ethidium bromide. Under these conditions the Gaussian distributions of topological isomers of both supercoiled and relaxed DNA migrated as discrete bands. The separation of these DNAs was optimized by varying the concentration of electrode buffer. Electrophoresis in the presence of 160 mM Tris-acetate, pH 8.3, 4 mM EDTA resulted in a 20-fold increase in the separation of relaxed and supercoiled DNA relative to electrophoresis in 40 mM Tris-acetate, pH 8.3, 1 mM EDTA.