A loxP site was inserted into the 5UTR of exon 1, an FRT-flanked PGK-neomycin selection cassette was inserted after exon 2, followed by a loxP site and a third loxP site downstream of exon 3. Flp-mediated recombination removed the selection cassette and cre-mediated recombination deleted exons 1-3. Western blot analysis confirmed absence of protein.