The targeting construct introduced into exon 3 an FRT site, lacZ reporter gene, loxP site, neomycin resistance cassette, FRT site and loxP site. An additional loxP site was inserted downstream of exon 5. Flp-mediated recombination removed the reporter and selection cassettes. Cre-mediated recombination removed exons 4 and 5. (J:263129)