Exons 6-10 were replaced with a construct containing exons 6 and 7, a loxP site, a minigene containing exons 8-11, a polyadenylation STOP sequence, a FRT-flanked neomycin resistance gene, a second loxP site, a mutated exon 8, and exons 9-10. The mutated exon 8 contains a C to T mutation at position 1402 and a G to T mutation at position 1404, resulting in an arginine to cysteine change at amino acid 468. The R468C mutation corresponds to the human R465C mutation, frequently detected in primary tumors. The mutant is expressed only after cre-mediated recombination.