A construct containing a loxP site, exon 8, a lox2272 site, FRT-flanked neomycin resistance gene cassette (PGK-neo), an inverted exon 8 containing an A to T mutation at position 983 which results in a lysine to methionine substitution at amino acid 328, a loxP site and lox2272 site replaced exon 8. Flp-mediated recombination removed the PGK-Neo. Cre-mediated recombination removed the wild-type floxed exon 8 and flipped the mutant exon in the correct orientation so it is expressed. (J:306976)