An FRT-flanked PGK-neomycin selection cassette and a loxP site were inserted upstream of exon 4 and a second loxP site was inserted downstream of exon 4. The neomycin selection cassette was removed via flp-mediated recombination. Exon 4 was deleted via cre-mediated recombination. Western blot analysis confirmed absence of protein in islets. (J:279170)