Sequence coding for an N-terminal hemagglutinin (HA) tag was inserted into exon 1 immediately after the ATG start codon, isoleucine codon 73 (ATC) in exon 3 was changed to threonine (p.I73T), and an FRT site flanked neomycin resistance gene and gb2-promoter-driven kanamycin resistance gene cassette into intron 1. The neo/kana cassette was removed through subsequent Flp-mediated recombination. (J:267027)