Exons 1 and 2 were replaced with a neomycin selection cassette in reverse orientation. This removed the transcriptional and translational start sites and the first 54 amino acids including the secretion signal peptide and helix A. mRNA was not detected in pancreatic islets, small intestine, liver, spleen, kidney, and brain by RT-PCR. Western blot analysis of pancratic islets demonstrated the absence of full length protein.