“…Sucrose gradient centrifugation. Five-milliliter linear 20 to 31% sucrose gradients made in either 1 M NaCl, 0.05 M Na2 ethylenediaminetetraacetic acid, pH 7.5, or 1 M NaCl, 0.01 M Na2 ethylenediaminetetraacetic acid, and 0.3 N NaOH, pH 12.5, were used to characterize the CCC DNA isolated from these gonococcal strains. The reference plasmid was [3H Ithymidine-labeled Col El DNA, isolated from Escherichia coli JC 411, which has sedimentation coefficients of 23S and 17S, for the CCC and open-circular molecules, respectively, in neutral sucrose gradients (3).…”