The Wtsi targeting vector PPGS00100_B_C02 was used for gene targeting. Exon 4 was flanked by loxP sites. In addition, an FRT site and a beta gal construct separated by a third loxP site from a neomycin sequance and an additional FRT site was inserted in intron 3. The beta gal and neomycin were subsequently removed by expression of flp recombinase leaving exon 4 flanked by loxP sites. (J:217296)