Figure 2.

In vitro recombination experiments performed on native loxP sites or modified by the introduction of a phosphorothioate at the protein cleavage site. Lanes marked ‘48’ contain the 48mer loxP oligomer. Lanes containing the recombinase are indicated with ‘Cre’. The 37mer loxP oligomer is present in lanes marked with ‘5/9’ (unmodified DNA), ‘2/9’ (phosphorothioate on the top strand), ‘5/6’ (phosphorothioate on the bottom strand) and ‘2/6’ (phosphorothioate on top and bottom strands). Due to the presence of overhangs on the 37mer loxP site used for crystallization experiments, two different sizes of recombinant DNA are obtained with unmodified loxP site, corresponding to a 42mer and a 43mer oligomers. No recombinant DNA was detectable in our conditions when a phosphorothioate was present either on the top or the bottom strand.