Human topoisomerase I – DNA relaxation assay
Human topoisomerase I relaxes supercoiled plasmid DNA to form relaxed DNA. The Human DNA topoisomerase I assay is based on the principle that the supercoiled DNA and relaxed DNA yield different fluorescent intensity when interact with fluorescence dye H19. The relaxed DNA suppresses the fluorescent intensity much more than the supercoiled DNA. Therefore, when the supercoiled DNA is converted into its relaxed form, the fluorescent signal decreases. The change of fluorescence intensity is used to measure the relaxation reaction.