An FRT and LoxP flanked neo cassette was inserted upstream of exon 18 and a loxP site was inserted downstream of exon 18 via homologous recombination. Cre mediated recombination removed exon 18. RT-PCR analysis detected the presence of a lower molecular weight product. Western blot analysis detected a small amount of truncated protein in brain lysates from homozygous mice. (J:183239)