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…

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In this paper researchers have devised a very clever strategy to evaluate the genesis of topological domains. The basic idea is to design high affinity DNA binding sites for specific proteins as tandem copies within a single plasmid. Then, they tested whether it was possible to divide the plasmid into protein defined domains of constrained topological segments (or create topological barriers). This is a nice inroad to understand how topological domains can be propagated in linear chromosomes in eukaryotes. In…

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