Minimal piggyBac vectors for chromatin integration

We describe novel transposon piggyBac vectors engineered to deliver transgenes as efficiently as currently available piggyBac systems, but with significantly less helper DNA co-delivered into the host genome. To generate these plasmids, we identified a previously unreported aspect of transposon biology, that the full-length terminal domains required for successful plasmid-to-chromatin transgene delivery can be removed from the transgene delivery cassette to other parts of the plasmid without significantly impairing transposition efficiency. This is achieved by including in the same plasmid, an additional helper piggyBac sequence that contains both long terminal domains, but is modified to prevent its transposition into the host genome. This design decreases the size of the required terminal domains within the delivered gene cassette of the piggyBac vector from about 1500 to just 98 base pairs. By removing these sequences from the delivered gene cassette, they are no longer incorporated into the host genome which may reduce the risk of target cell transformation.