A cDNA encoding for exons 5 - 7 plus the UTR replaced a genomic region including all of exon 5. In the cDNA, exons 5 and 6 contain K to R substitutions at positions 268 and 293 (K268R, K293R). In addition, a floxed neo selection cassette was inserted downstream of the cDNA then removed via cre-mediated recombination. (J:312317)