Topoisomerase I activities in L-1210 cell nuclei.

Topoisomerase was extracted from L-1210 nuclei by 0.35 M sodium chloride Extract fractionation by molecular weight revealed two activities. The activities were quantitatively determined using a technique based on the electrophoretic separation of 3H-labelled DNA product from substrate. This technique enables the determination of topoisomerase activity in extracts where nuclease activity is also present.