DNA Topoisomerase I catalyzes 4 kinds of reactions: catalyzes the relaxation of negative supercoiled DNA. Form knots (Knotting) and untie knots (Unknotting) in single-stranded circular DNA molecules. Catalysis of circular single-stranded DNA with complementary base sequences to form double-stranded closed circular DNA molecules. When one of the two circular double-stranded DNA molecules has a DNA strand incision, a linking reaction (Catenation) or reverse reaction (Decatenation) of the two molecules occurs. The complete DNA topoisomerase I(E.coli) holoenzyme is a protein with a molecular weight of 97kDa. This product is the topA gene (E.coli) was expressed in E.coli, after several purification and isolation. Suggestions for use: structural transformation and analysis of DNA.