Exon 11 was replaced with a modified exon 11 in which nucleotide substitutions (AGA to GCC) result in the amino acid substitution of alanine for arginine at position 579 (R579A). This mutation results in a constitutively active protein. Cre-mediated recombination removed the floxed neomycin resistance cassette inserted downstream of the modified exon 11. (J:200838)