Figure 6.

AP site-induced covalent Topo IV–DNA complexes cannot inhibit the functional activities of replicative helicases. Strand displacement assays for the DnaB (A and B) and T7 Gene 4 proteins (C and D) were performed as described in Materials and Methods. Reactions were incubated in the absence or presence of Topo IV. No norfloxacin was present. The DNA products were analyzed by electrophoresis through either 1% native agarose gels (A and C) or 9% native polyacrylamide gels (B and D). Relative amounts of strand displacement were as follows. For DnaB (A): lane 3, 84.0%; lane 4, 74.0%; lane 5, 90.5%; lane 6, 76.4%; lane 7, 89.7%; lane 8, 76.9%. For T7 Gene 4 (C): lane 3, 90.9%; lane 4, 90.7%; lane 5, 91.5%; lane 6, 88.4%; lane 7, 93.7%; lane 8, 91.4%. Lanes 1 and 2 in all panels were heat-denatured and native T440(0), respectively. Experiments were repeated twice and representative results are shown. Error range for DnaB and T7 Gene 4 helicase assays were 5 and 4%, respectively. Abbreviations are as in the legend to Figure 2.