The targeting construct inserted a loxP site upstream of exon 1 and an FRT-flanked neomycin selection cassette and loxP site in the 3' UTR in exon 2. Subsequent flp-mediated recombination removed the neo cassette and cre-mediated recombination deleted exon 1 and most of exon 2, leaving the 3' end of the 3' UTR. (J:231297)