A Trojan exon encoding a T2A peptide followed by the TI{2A-p65(AD)::Zip+} hemidriver has been inserted in an intron of vg. The T2A-TI{2A-p65(AD)::Zip+} sequence is flanked by a pair of FRT sites, which in turn are flanked by a pair of inverted attP sites. This allows for excision of the T2A-TI{2A-p65(AD)::Zip+} exon (using FLP recombinase) or for replacement of the sequence between the attP sites with DNA from a compatible donor plasmid (where the sequence to be inserted is flanked by inverted attB sites) through recombination-mediated cassette exchange (RMCE) driven by the phiC31:int integrase.