Exons 10 and 11 were flanked by loxP sites. An FRT-flanked neomycin selection cassette was inserted after the first loxP site, upstream of exon 10, and was removed via flp-mediated recombination. Exons 10-11 encode for the second substrate-binding site, the iron-binding site, part of the p450 domain, and the polyA signal. (J:274566)