The gene locus produces three different transcript variants that express the same 35-kDa protein but differ in their upstream untranslated region (UTR). A gene trap inserted downstream of "exon a", a non-coding exon that lies 27 kb upstream from the first coding exon. This insertion disrupted the UTR for one transcript variant of the gene locus but left intact two other transcript variants. Homozygotes for this allele are hypomorphs with the only strong gene expression occurring in the intestinal tract while wild-type mice have strong gene expression in numerous tissues including heart, kidney, liver, lung, stomach, and the intestinal tract.