FIGURE 3.

The reduced activities of Top1-clamp⁵³⁴ and Top1-clamp⁴⁹⁹ are partially suppressed by DTT. Equal concentrations of homogenous preparations of Top1, Top1-clamp⁵³⁴, and Top1-clamp⁴⁹⁹ were serially 10-fold diluted and incubated in plasmid DNA relaxation assays in the presence or absence of 10 mm DTT and the indicated concentration of KCl. After 1 h at 37 °C, the extent of plasmid DNA relaxation was assessed by agarose gel electrophoresis followed by EtBr staining. Lane C, plasmid DNA control. R and (-), the positions of relaxed and supercoiled DNA, respectively.