A portion of exon 2 and all of exon 3 was replaced with a neomycin selection cassette. The deleted region encoded approximately one and one half of the amino-terminal TNFR-like cysteine-rich domain, comprised of residues 34 through 96. Northern blot analysis confirmed the absence of normal transcript, while the results of a Western blot analysis of intestinal lysates using antibodies raised against the extracellular domain of the endogenous protien indicated a lack of protein.