Dynamics of DNA Supercoiling

A catalytic turnover of supercoiled DNA (scDNA) transformation mediated by topoisomerases leads to the changes of the linking number (Lk) of the polymeric substrate by 1 or 2. While a substrate of the topoisomerisation reaction is chemically identical to its product, even single catalytic event results in the quantum leap in the scDNA topology. A continuous non-disturbing assay for measurement of kinetics of the scDNA topoisomerisation was lacking. The intrinsic connections of DNA topology, its hydrodynamics and optical anisotropy, studied in this chapter allowed the use of flow linear dichroism technique (FLD) for continuous monitoring of scDNA topoisomerisation reaction. This approach permits studying the kinetics of DNA transformation catalysed by eukaryotic topoisomerases I and II, mechanistic properties of these enzymes and their interactions with anti-cancer drugs.