The targeting vector was designed (by site-directed mutagenesis) to insert the arginine to histidine amino acid substitution at position 1207 (R1207H) (human 1205) into exon 24 and place a loxP site upstream of exon 24, followed by an FRT-flanked neomycin cassette and a loxP site downstream of exon 28. Flp-mediated recombination removed the neomycin cassette.