An enhanced green fluorescent protein (EGFP)-STOP cassette, followed by a loxP-flanked neomycin selection cassette (neo) in reverse orientation was inserted 3' of the promoter IV exon. Promoter IV drives expression of a fusion transcript composed of GFP and the endogenous coding sequence. However, only a GFP protein is translated from this transcript because of the GFP stop codon. Kainic acid fails to induce the normal promoter IV transcript and fails to induce an increased production of the normal protein product.