The signal sequence coding region of exon 2 was replaced by preprotrypsin signal sequence followed by triplicated FLAG epitope coding sequence. Exons 2 and 3 were flanked by loxP sites and an FRT-flanked neomycin resistance cassette was placed in intron 2. Flp-mediated recombination removed the neo cassette. This allele is hypomorphic. (J:125344)