Purification of DNA Topoisomerase II from Drosophila melanogaster

To characterize properly protein function and enzymatic activity, it is highly desirable to perform experiments with purified protein preparations. This is especially true in the case of topoisomerase II, because many of the enzymatic assays critical to the topoisomerase field (such as DNA cleavage) require enzyme levels in excess of the DNA substrate (1 -5 ). As a result of the high topoisomerase II concentrations routinely used in these assays, even minor contamination by topoisomerase I or other enzymes that affect DNA structure (such as nucleases) may pose significant technical problems or may lead to erroneous conclusions.