pTRIDENT vector backbones encode a bacterial ampicillin resistance and origin of replication (ori) Figure 2 . Examples for multicistronic expression in mammalian cells: pTRIDENT1 and pQuattro-tTA. Both vectors allow tetracycline-regulated expression of all transgenes. Since pQuattro-tTA encodes all genetic elements for regulated gene expression in its multicistronic expression unit, pQuattro-tTA allows autoregulation and can be used to achieve one-step regulated expression the genes of interest in any cell line where the internal ribosomal entry sites of polioviral origin function (IRES, CITE).