The gene trap vector containing a beta-galactosidase/neomycin gene was inserted within intron 18. RT-PCR confirmed that mutants contained a truncated mRNA resulting from the splicing of exon 18 to the beta-geo cassette using the cryptic splice site from the gene trap vector. The resulting protein is predicted to be inactive as it lacks the 129 amino acids of the tail domain. (J:121799)