A loxP site was inserted upstream of exon 1 and a construct, containing an FRT site V6.5, polyA sequence, loxP site, neo cassette, FRT site and loxP site, was inserted downstream of exon 2 via homologous recombination. Recombinase mediated recombination removed the polyA sequence, neo cassette and exons 1 and 2. (J:256465)