pEPI-derived plasmids generated in this study. A schematic picture of the four types of vector backbones is depicted in the upper panel: pEPI-1 (A), pEPito (B), pEPI-1-ΔMARS (C), or pEPito-ΔMARS (D). All vectors contain either the CMV-IEP or the hCMV/EF1P promoter element. Depending on the experiment, three different transgenes have been used: an EGFP-BSD cassette connected via an internal ribosomal entry site module (EGFP-IRES-BSD), a Firefly luciferase (Luc), or an EGFP-luciferase fusion protein (EGFP::Luc). All 13 different vectors have been constructed, propagated, and amplified in E.coli DB3.1λpir. (E) Additional information regarding the different vectors. The vector pEPI-1- [CMV-IEP]- [Luc] has been recently published as pEPI-Luc . This figure does not claim proportional correctness.