A targeted vector containing a floxed "mini-cDNA" including a splice acceptor and normal cDNA sequence for exons 15-17, followed by a frt-flanked neo cassette and a third loxP site, inserted into intron 14, and a nucleotide change causing a D620N mutation in the inherent mouse gene sequence 3' of the insertion. The polyadenylation signal sequence at the end of the mini-cDNA prevents expression of the D620N mutation. Flp-mediated recombination removed the neo cassette. Cre-mediated recombination removed the "mini-cDNA" sequence and allows expression of the D620N mutation. (J:274797)