Part of exon 1 and all of exon 2 was replaced with an IRES-BetaGal-polyA-PGK-neo cassette via homologous recombination. Western blot of cerebral membrane fractions and immunohistochemical staining of pancreas sections from homozygous mutant animals did not detect protein product. Unexpectedly, lacZ staining was not detected in mutant animals.