A Topological Treatment of Recombination and Topoisomerases
This extract was created in the absence of an abstract.
Excerpt
A feature of several site-specific recombination systems currently under study is that they can reduce the supercoiling of the substrate and produce knots or catenanes in addition to rearranging DNA sequences. The topological changes can be analyzed to reveal specific information about the mechanism of recombination.
The change in the topology of circular DNA during supercoiling or relaxation by a topoisomerase is well-defined as a change in the linking number (Lk) of the DNA. No such index of topological structure exists to measure the topological changes made during knotting or catenation by either topoisomerases or recombination enzymes.
We describe an index called linkage (Lg) that can be applied uniformly to knots, catenanes, supercoils, and double-helical twist. It is based on counting the crossings, or nodes, in a plane projection of a DNA molecule. For unknotted single rings of DNA, Lg = Lk. For knots and catenanes, Lg also includes the...
