CRISPR genome editing and off-target effects

—programmable changes in genomes. One of the main challenges facing the use of genome editing proteins is that they have some off-target activity if you just take them from nature, meaning that they will hit your target, but they'll also hit other targets that aren't your target. And generally, it's not a wise idea, either for research or therapeutic purposes, to modify semi-randomly in the genome. So we used the PACE system to evolve genome editing proteins that were much more specific for maintaining their on-target activity, but getting rid of their off-target activity than the natural ones. And we did this by using positive selection pace to constantly enforce a Darwinian selection pressure that they had to bind to the target DNA sequence, and using negative selection pace, something I didn't have a chance to talk to, to get rid of their ability to bind to the off-targets. So P3 is this essential protein that the phage need to replicate. There's a sort of dark parallel universe, Bizarro World cousin called P3 neg that poisons P3.