A loxP site was inserted upstream of the coding region. An FRT-flanked neo cassette, a loxP site, a modified coding region containing nucleotide substitutions that result in the amino acid substitution of phenylalanine for serine at position 17 (S17F), and an IRES-EGFP were inserted downstream of the coding region. Flp-mediated recombination removed the neo cassette. Additional cre-mediated recombination is required to remove the endogenous coding region and allow for expression of the modified one. (J:166732)