Exon 4 was replaced with a modified exon in which nucleotide substitutions result in the amino acid substitution of alanine for serine at position 362 (S362A). Flp-mediated recombination removed the floxed neo cassette inserted downstream of the endogenous polyadenylation sequence and left an EGFP gene with a 5' loxP site intact. (J:175064)