Figure 9 :Function of topoisomerases in the cell-free system with E. coli cell extract. (A) Electrophoresis of the relaxed supercoiled pBR322 DNA treated with four different E. coli topoisomerases in the presence of cell extract. Lane a, linear DNA marker (0.3 µg); lane b, supercoiled DNA marker (0.3 µg); lane c, supercoiled DNA with cell extract; lane d, relaxed supercoiled DNA, which was the product of supercoiled DNA treated with topoisomerase I; lane 1, relaxed supercoiled DNA with cell extract; lane 2 relaxed supercoiled DNA treated with topoisomerase I with cell extract; lane 3, relaxed supercoiled DNA treated with gyrase with cell extract; lane 4, relaxed supercoiled DNA treated with topoisomerase III with cell extract; lane 5, relaxed supercoiled DNA treated with topoisomerase IV with cell extract. (B) AFM images of the hemicatenated dimer plasmid pBR322 DNA. The dimer was prepared by Topo IV relaxed pBR322 DNA (Figure 6, lane 4) treated with Topo I. Arrows show the intermolecular single strand crossing (hemicatenation).