Two sequence cassettes have been inserted into the endogenous Vmat locus: first, a stop cassette flanked by RSRT sites has been inserted in between coding exons 5 and 6 and second, six tandem copies of the Tag:V5 tag has been inserted in-frame within exon 8 (common to both A and B isoforms). 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 Vmat.