A loxP site was inserted upstream of exon 2. An FRT-flanked neomycin resistance cassette with a 5' loxP site was inserted downstream of exon 4. An IRES-nlacZ was inserted into exon 6. Flp-mediated recombination removed the neomycin resistance cassette and left exons 2 through 4 floxed and the lacZ reporter intact.