One loxP site was inserted into intron 13 and the other, with a PGK-neo cassette, into intron 14. Northern blot analysis revealed that RNA expression in the intestinal tract of homozygous mutants was about 30% of that in wild-type mice. Protein expression in the colon of homozygotes by immunohistochemistry was indistinguishable from that of wild-type mice. Western blot analysis of lysates from mouse embryo fibroblasts showed reduced expression of the protein.