The targeting construct introduced nucleotide substitutions in exons 15 and 17 that result in the amino acid substitutions of glutamic acid for arginine and lysine at positions 461 and 542, respectively (R461E, K542E). These mutations disrupt interaction with the transactivation domain of E2f1. Cre-mediated recombination removed the floxed neomycin resistance cassette inserted upstream of exon 17. (J:215358)