Exon 1 was replaced with a neomycin selection cassette. RT-PCR of RNA isolated from the liver of homozygous mice using primers directed against exon 1 and exon 4 shows that there was no detectable message expressed from this allele. Immunoblotting of liver lysates and immunohistochemistry of liver sections from homozygous mice indicates that the encoded protein is not detectable in homozygous mice.