An FRT site flanked neomycin resistance gene cassette and a loxP site flanked chicken transcriptional enhancer element A that contains specific mutations in the Egr2 binding sites that prevent binding of wild-type Egr2 and instead allow binding of a mutant Egr2 (Krox20) protein, and an F3 site flanked mouse element A replaced the wild-type autoregulatory element A. Flp-mediated recombination removed the F3 flanked mouse element A and the neo cassette such that the chicken element A is expressed. (J:277269)