Fig. 3.

Recombination reactions catalyzed by Cre and Flp. The outcome of the recombination reaction is determined by the relative orientation of target sites. Inverted target sites in the same linear molecule dictate inversion of intervening DNA (a). Recombination between a target site located in a genomic address and an identical target site present in a circular DNA molecule results in insertion of circular DNA (b; thin arrow). The intramolecular recombination (thick arrow) is favored over the intermolecular reaction (thin arrow) (b). RMCE involves recombinase-mediated insertion and excision reactions, which lead to mutual exchange of the DNA between target sites (c). The inclusion of mutated target sites makes the recombination reaction irreversible