A targeting vector was designed to insert a loxP site upstream of exon 2, and a second loxP site, followed by a frt-flanked neomycin resistance (neo) cassette, downstream of exon 3. Cre-mediated recombination removed exon 2, exon 3 and the neomycin reistance cassette. Western blot analysis confirmed the absence of transcript expression in ES cells. (J:197442)