Exon 2 was replaced with a human cDNA encoding exons 2-4, intron 4, exon 5, intron 5, and fusion of exons 6-9 with an frt-flanked hygro cassette. The sequence was flanked by an attB53 site at the 5' end and an attP50 site at the 3' end. Germ line, flp mediated recombination was used to remove the hygro cassette. The absence of the endogenous transcript expression was confirmed by qPCR on liver and small intestine extracts.