Alexander Vologodskii

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  On Simplification of DNA Topology by Type II DNA Topoisomerases
  Alexander Vologodskii
  Type II DNA topoisomerases can change DNA topology by catalyzing the passing of one double-stranded DNA segment through another. In 1997 Rybenkov et al. unexpectedly found that the enzymes can greatly reduce, up to hundred times, the fractions of knotted and linked circular DNA molecules comparing with the corresponding equilibrium values. The phenomenon of topology simplification attracted a lot of attention because it was very difficult to understand how small enzymes could determine topology of large DNA molecules. It seems clear now that the only way for the topoisomerases to achieve topology simplification is to use the fact that the probability of some specific local conformations of DNA segments depends on DNA topology. Although great progress has been made in understanding the phenomenon, some features of it are not explained by the existing models. To eliminate the discrepancy with the experimental data we suggest here a new model of the enzyme action.