Exon 1 was replaced with an FRT-flanked STOP cassette and a modified exon 2 lacking the 45 nucleotides correspondihng to the signal sequence. Flp-mediated recombination removed the FRT-flanked neomycin resistance cassette inserted downstream of exon 3. Cre-mediated recombination is required to achieve expression of the intracellular isoform of the protein. This allele cannot produce the soluble isoform. (J:259332)