Figure 4: Restricted nicking by endonuclease Nb.Bpu10I promotes untying of pBR322 DNA. (A) Electrophoresis of plasmid pBR322 DNA treated with Nb.Bpu10I for various time. Lane 1, supercoiled DNA control (0.1 µg); lane 2, 1min; lane 3, 5min; lane 4, 10min; lane 5, 30min; lane 6, 60min, lane 7, linear DNA marker. OC, open circular DNA; L, linear DNA; SC, supercoiled DNA; SCD, supercoiled circular dimer of pBR322 DNA; RD, relaxed circular dimer of pBR322. (B) AFM image of pBR322 DNA treated with Nb.Bpu10I for 1min. (C) AFM image of pBR322 DNA treated with Nb.Bpu10I for 10min.