Figure 3.

DNA cleavage activities of wild-type, GrlA^S81F, and GrlA^S81Y topoisomerase IV. The ability of wild-type (WT, black squares), GrlA^S81F (S81F, red circles), and GrlA^S81Y (S81Y, blue triangles) topoisomerase IV to cleave negatively supercoiled pBR322 plasmid DNA is shown. Assays were carried out in the presence of 1 mM CaCl₂. Error bars represent the standard deviation of three or more independent experiments. The inset shows an agarose gel of a typical DNA cleavage assay mediated by wild-type topoisomerase IV in the absence of divalent metal ion (None) or in the presence of Mg²⁺, Ca²⁺, or Mn²⁺. The positions of negatively supercoiled (replicative form I, FI), nicked (replicative form II, FII), and linear (replicative form III, FIII) plasmids are indicated.