Two sequence cassettes have been inserted into the endogenous VGAT locus: first, a stop cassette flanked by RSRT sites has been inserted in the intron (this cassette includes an upstream splice acceptor followed by translation stop codons in all three reading frames) and second, nine tandem copies of the Tag:V5 tag have been inserted in-frame near the beginning of exon 2. The stop cassette prevents expression of the Tag:V5 tag, but in the the presence of RSR recombinase it is excised, allowing expression of Tag:V5-tagged VGAT.