The targeting vector was obtained from the KOMP repository at UC Davis and is composed of an FRT site followed by lacZ sequence and a loxP site. The first loxP site is followed by neomycin resistance gene, SV40 polyA, a second FRT site and a second loxP site. A third loxP site is inserted downstream of exon 3. The critical exon 3 is thus flanked by loxP sites. (J:244278)