Exon 2 was replaced with a floxed neo cassette and a modified exon 2 with nucleotide substitutions that result in the amino acid substitutions of arginine for lysine at positions 219, 242, 245, 259, 262, 271, 291 (K219R, K242R, K245R, K259R, K262R, K271R, and K291R). These mutations produce a constitutively deacetylated allele. Cre-mediated recombination removed the neo cassette.