Overview of Cre Recombinase

Taken from from the P1 Bacteriophage, Cre recombinase is widely used as a site specific DNA recombinase. The protein functions by binding to LoxP as a dimer, then two bound dimers coming together as a tetramer, creating a Holiday Junction, and finally breaking, recombining, and re-ligating the DNA back together.
One useful property of Cre recombinase is its ability to recombine DNA at very low concentrations of active protein. Since the ultimate goal is to send Cre recombinase through exosomes, the amount of Cre recombinase entering the sender cell will likely be small, but as mentioned earlier, that shouldn't be a problem, as it doesn't take very many Cre molecules to trigger a recombination event.