The targeted construct replaced the coding sequence of exon 1 with the coding sequence from human exon 1, a loxP site, an FRT-flanked neomycin resistance cassette, the human sequence for exon 3 through 13, a FLAG-tag, the mouse 3' untranslated region, an F3-flanked puromycin resistance cassette, a loxP site and polyadenylation sequence. Flp-mediated recombination removed both selection cassette. (J:219255)