 The strand exchange is then followed by the religation (Stark et al., 1992).Recombination between two directly repeated res sites separates, or resolves, the "cointegrate" into two original molecules, each one now containing a copy of the Tn3 transposon.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).