Site-specific Recombination in Transposition and Plasmid Stability

Since the early characterization of the site-specific integration and excision system of bacteriophage λ, several other site-specific recombination systems have been described in detail. All of these possess a specific recombination site and an adjacent gene specifying the recombination enzyme. In all characterized cases, recombination appears to be a conservative breakage-reunion reaction in which the recombination enzyme also has the properties of a type-I topoisomerase. Although one might expect site-specific recombination reactions to be freely reversible and to act on all combinations and orientations of recombination sites (direct and inverted repeats; in the same and separate DNA molecules), they often show preferred combinations and orientation of site in vivo and in vitro. In the case of λ, this is at least partly the consequence of having asymmetric sites (attP and attB) that recombine to give a new pair of hybrid sites (attL and attR), Different enzyme complexes act on the...