A mutation was engineered to change isoform 2 lysine codon 107 in exon 3 (AAA) to arginine (AGA)(p.K107R) and an FRT site flanked neomycin resistance gene cassette was inserted into intron 3. The neo cassette was removed through subsequent flp-mediated recombination. The mutation prevents SUMOylation of the residue in the encoded peptide. (J:269302)