A targeting construct was designed to change the seven C-terminal lysines to arginine (p.K367R, p.K369R, p.K370R, p.K378R, p.K379R, p.K383R, p.K384R). A loxP site flanked neomycin resistance gene cassette was included in the vector, which was electroporated into ES cells carrying a self-excising cre recombinase gene. (J:100189)