An FRT-flanked puromycin resistance cassette with a 5' loxP site was inserted upstream of exon 2. An additional loxP site was inserted downstream of exon 2. Flp-mediated recombination removed the selection cassette. Cre-mediated recombination removed exon 2. Western blot analhysis confirmed the absence of protein expression in the liver, kidney and heart. (J:228816)