A G to A nucleotide change at position 49 (c.49G>A) was introduced in exon 3 resulting in a glutamate to lysine substitution at amino acid 17 (p.E17K). A loxP-flanked lacZ and neomycin resistance gene fusion cassette containing a transcription termination signal was inserted upstream of exon 3. Cre-mediated recombination in the ES cells removed the lacZ/neomycin cassette resulting in the expression of the mutant protein. (J:293971)