The targeting vector is designed to insert loxP66 and loxP71 inward facing sites flanking the promoter and first exon of the gene (from -561 to +538bp); they are inverted relative to their normal endogenous orientation. An FRT-flanked neomycin resistance (neo) cassette was inserted in intron 1, between exons 1 and 2. Flp-mediated recombination removed the FRT-flanked neo cassette. (J:261728)