The targeting vector contains an FRT-flanked splice acceptor/IRES/lacZ/puromycin fusion gene followed by a loxP site inserted upstream of exon 3 and a second loxP site followed by an F3-flanked neomycin cassette inserted downstream of exon 6. Flp-mediated recombination removed the FRT-flanked lacz/puro and neo cassettes leaving exons 3 through 6 floxed. (J:266163)