The targeting vector is designed to insert loxP sites flanking the promoter and first exon (at positions -561 bp and at +538 bp relative to the major transcriptional start site). 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:114621)