A rapid in vitro method to flip back the double-floxed inverted open reading frame in a plasmid.

We have presented an in vitro protocol to invert the ORF in FLEX based plasmids. This protocol is simple and highly efficient. Thus this method expends current molecular biology toolbox. We also demonstrate that the recombination between Lox2272 sites is much less efficient than wild type LoxP sites. This result has important implication for evaluating the efficacy of FLEX switch in biological systems and provides a rationale for future development of higher efficiency LoxP mutants.