The phospho-acceptor sites Ser468 and Ser485 located in exon 15 were mutated to alanine (S468A and S485A). A wild-type copy of exon 15 floxed by loxP sites was inserted into intron 14-15 upstream of the exon 15 splice acceptor followed by a polyadenylation signal. A FRT-flanked neomycin selection cassette was inserted into intron 14-15. FlpE-mediated recombination removed the neo cassette. (J:296139)