Binding between DNA topoisomerase II and plasmid DNA can be measured using a variety of methods. The electrophoretic mobility shift assay (EMSA) is an efficient and inexpensive means for examining DNA affinity. This method relies on the principle that increasing concentrations of enzyme will result in more topoisomerase bound to DNA. As more binding occurs, the DNA migration in an agarose gel is decreased causing an upward “shift” in the DNA molecules when visualized in the gel. This shift can be compared across a range of concentrations to establish binding parameters under varying circumstances such as substrate type, the presence of a compound or drug, incubation time, or other conditions.