A mutation was engineered to change glycine codon 422 to a serine codon (p.G422S). This change renders the peptide subject to phosphorylation at that residue and thus makes it more similar to homolog Crebbp, which has a serine at the equivalent position (S436). A self-excising ACN cassette (comprising a loxP site, testes-specific elements of mouse Ace gene, a modified Cre gene with SV40 intron and HSV polyadenylation signal, a neomycin resistance gene cassette, and a second loxP site) was inserted into intron 5. (J:278697)