Exons 3-5 were flanked by loxP sites and a neomycin resistance cassette flanked by FRT sites and a puromycin resistance cassette flanked by F3 sites were introduced in intron 2 and intron 5, respectively. Flp-mediated recombination removed the selection markers. Exons 3-5 were deleted via cre-mediated recombination. (J:282882)