Fig 1. Schematic representation of the conditional Cre-Flex LV.

The cDNA cassette is flanked by one pair of WT loxP sites (closed arrowheads) and one pair of mutant loxm2 sites (open arrowheads). In the presence of Cre recombinase, the DNA sequence between opposing sites is inversed (Flip), resulting in the positioning of two homotypic sites in the same orientation. The DNA sequence that is flanked by similarly oriented sites is excised (Excision). Cre-mediated inversion can start at the loxP or the loxm2 sites, but will always result in the same final product after Cre-mediated excision. The end product is an inverted DNA sequence, flanked by two heterotypic sites that cannot recombine with one another thereby preventing further inversions.