Tn3 transposon

Shapiro (1978)[1] proposed the following mechanism for this process: The diagrams on the right illustrate the way in which the positions of the cleavages lead to the replication of certain regions once the plasmids have fused.

At recombination, two directly repeated res sites with resolvase dimers bound to each sub-site, come together to form a large complex structure called the synaptosome.

After the tetramer is formed it becomes activated and the top and bottom DNA strands are simultaneously cleaved in the middle of the site I with a 2bp overhang.

After resolution these two molecules remain linked as a simple two-noded catenane which can be easily separated in vivo by a type II topoisomerase (Grindley 2002).

Wild type resolvase system absolutely requires a supercoiled substrate and that the recombination sites are oriented in a direct repeat on the same DNA molecule.

[4][9] Hyperactive resolvase mutants, if further developed, could become an alternative to Cre and FLP, the most commonly used recombination systems in molecular biology to date.