Topo II and Topo I are not Equivalent Topological Adjustment Machines in vivo
In a recent report in Nucleic Acids Research, researchers provide evidence that topoisomerase I and II perform similar functions in vitro (relaxation of supercoiled DNA); however, the in vivo situation is very different. There are of course non-overlapping activities of type I and II enzymes, specifically, the latter are cell cycle regulated and provide decatenase activity which is essential for life. Still, topo enzymes provide other key functions that attend all aspects of template activation. From genetic complementation studies, topological…