A targeting vector was designed to insert a loxP site into intron 11, a loxP-FRT-flanked neomycin cassette into intron 13 and a G844D point mutation into exon 15. The mutation results in a G to A change at nucleotide 2531 altering the corresponding amino acid from glycine to aspartic acid at position 844. FLP-mediated recombination removed the FRT-flanked neo cassette.