The targeting vector was designed to insert a point mutation (G365C) into exon 5 by site-directed mutagenesis. A loxP site was inserted upstream of exon 5 and an FRT-flanked neomycin cassette followed be a second loxP site was inserted downstream of exon 6. The mutation results in a change in amino acid 122 from tryptophan to serine. Flp-mediated recombination removed the FRT-flanked neo cassette leaving exons 5-6 floxed.