Abstract
We have transferred the prokaryotic γδ resolvase system to mammalian cells and present a comparative analysis of recombination by wild-type and two mutant resolvases (E124Q and E102Y/E124Q). Transient co-transfection assays using β-galactosidase as reporter for recombination reveal that episomal DNA does not contain a significant level of unconstrained negative supercoiling, since only mutant resolvases are recombination-proficient. We also show that the efficiency of recombination by the resolvase double mutant is comparable to that observed with Cre, which indicates that resolvase can be used as a new tool for controlled manipulations of episomal DNAs.