A gene trap cassette inserted into the first intron of the gene, and is predicted to truncate the encoded protein after lysine 32 (K31). The trap contains long terminal repeats (LTR), a splice acceptor (SA), a beta-Geo selective cassette containing beta-galactosidase and neo genes. A pair of FRT and loxP recombination signals in antisense orientation flanks the beta-Geo cassette.