Site directed mutagenesis within exon 2 generated a missense mutation (AG>GC) at codon 18 resulting in the substitution of serine with alanine (p.S18A). Serine 18 corresponds with human serine 15 of TP53 and this mutation prevents phosphorylation of the residue in the encoded peptide. A single loxP site remained in intron 3 after the inserted loxP site flanked neomycin resistance gene cassette was excised via Cre-mediated recombination.