An FRT site, EGFP, loxP site, neomycin selection gene, FRT site and loxP site were inserted upstream of exon 4 and a third loxP site was inserted downstream of exon 6. Flp-mediated recombination removed the EGFP and neomycin genes. Cre-mediated recombination deleted exons 4-6. (J:279152)