Relaxation complexes of plasmid DNA and protein. I. Strand-specific association of protein and DNA in the relaxed complexes of plasmids ColE1 and ColE2.

The ColE1 and ColE2 relaxation complexes of supercoiled DNA and protein were purified from Escherichia coli cells. Protein remains associated with the open circular DNA of these complexes after induction of relaxation with sodium dodecyl sulfate. The protein is associated specifically with the strand that possesses a site-specific break in the Co1E1 and ColE2 relaxed complexes. This protein remains associated with the DNA after centrifugation of the relaxed complex in a neutral or alkaline (pH 12.5) cesium chloride gradient or treatment with 8 M urea, 2 M NaSCN, 2M LiCl, 0.2 M sodium acetate, pH 4.6, and 70% formamide at 60 degrees.