An FRT-flanked neo cassette with a 5' loxP site was inserted upstream of exon 2, and an additional loxP site was inserted downstream of exon 3. Flp-mediated recombination removed the selection cassette. Cre-mediated recombination removed exons 2 and 3. Western blot analysis confirmed the absence of protein expression in the liver, spleen, thymus and lymph node. (J:188445)