Figure 3.

Generational changes of plasmid expression systems. Traditional plasmid DNA (pDNA) design usually contains two regions, one dedicated to plasmid propagation and the other to genetic cargo activity. However, in second generation plasmids, the vector is propagated and then processed with nucleases and ligated to remove the bacterial backbone. Alternatively, in third generation plasmids, no additional processing is required, as the plasmid propagation region is located to the intron in the transcriptional unit.