Topoisomerase II-Catalyzed Relaxation and Catenation of Plasmid DNA

Type II topoisomerases act by making a double-stranded break in a DNA segment, passing an intact DNA segment through the break, and resealing the break 1 –4 ). The DNA strand passage reaction of topoisomerase II can be either intra- or intermolecular. The enzyme relaxes supercoiled DNA in an intramolecular reaction, while it catenates and decatenates closed circular DNA in an intramolecular reaction (1 ,5 ). This chapter describes the relaxation and catenation reactions of topoisomerase II.