A targeting vector was designed to insert a double hemagglutinin (HA) tag into the 3'end of exon 6 of the gene. A loxP site, followed by a frt-flanked neomycin resistance cassette, was inserted upstream of exon 6, and a second loxP site was inserted downstream. FLP-mediated recombination in the germline removed the neomycin resistance cassette, leaving loxP sites flanking the HA-tagged exon 6. (J:272910)