A loxP site was inserted upstream of exon 1 and an FRT site flanked neomycin resistance gene cassette and a further loxP site were inserted in intron 1. Exon 1 and the neo cassette were removed through subsequent cre-mediated recombination, creating a null allele. Western blots confirm absence of protein product from the null allele in homozygous mice. (J:238174)