Before revision: The enzyme was derived from Cre recombinase through selective mutationfor the purposes of identifying HIV markers, which are not bounded by loxP sites and therefore disallow attempts at Through selective mutation, Cre recombinase which recognizes loxP sites are modified to identify HIV long terminal repeats instead.
After revision: Through selective mutation, Cre recombinase which recognizes loxP sites are modified to identify HIV long terminal repeats instead.