Using PCS6008_A_B12 from KOMP containing an FRT-lacZ cassette and loxP-flanked neomycin under the control of the human beta-actin promoter, SV40 poly A, a second FRT site and a second loxP site were inserted before exon 4. A third loxP site was inserted downstream of exon 4. Cre-mediated recombination removed exon 4.