A loxP site followed by FRT-flanked Neo cassette was inserted into intron 1 and an F3-flanked Puro cassette followed by a second loxP site was inserted into intron 2. Cre-mediated recombination removed exons 2 as well as the neomycin and puromycin cassettes. The null allele results in splicing of exon 1 to exon 3, which is expected to create a premature stop codon in exon 3 and give a 18-amino acid truncated product that lacks all functional domains. (J:275147)