A gene trap vector inserted into intron 2. The resulting fusion transcript of the first two exons of the gene (encoding the first 73 amino acids) with the beta-geo cassette produces a chimeric protein missing over 90% of the coding region, which is expected to be nonfunctional. Western blot analysis using an antibody recognizing an internal epitope near the C-terminus confirmed the absence of protein expression in homozygous mutant embryonic fibroblast cell lysates.