Minicircle

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Minicircle preparation from a parental plasmid. The parental plasmid contains two recombinase target sites (black half arrows). Recombination between these sites generates the desired minicircle (bottom right) together with the miniplasmid (bottom left). The hook on the red minicircle-insert stands for a scaffold-matrix attachment region (S/MAR-element), which allows for autonomous replication in the recipient cell.

Minicircles are small (~4kb) circular plasmid derivatives that have been freed from all prokaryotic vector parts.

For uses as transgene carriers for the genetic modification of mammalia cells, their preparation usually follows a two-step procedure:

production of a ´parental plasmid´ (bacterial plasmid with eukaryotic inserts) in 'E. coli'
induction of a site-specific recombinase at the end of this process but still in bacteria. These steps are followed by the
- excision of prokaryotic vector parts via two recombinase-target sequences at both ends of the insert
- recovery of the resulting minicircle (vehicle for the highly-efficient modification of the recipient cell) and the miniplasmid by capillary gel electrophoresis (CGE)

The purified minicircle can be transferred into the recipient cell by transfection or lipofection and into a differentiated tissue, for instance, by jet injection.

A novel addition to the field are self-replicating minicircles, which owe this property to the presence of a S/MAR-Element. Self-replicating minicircles hold great promise for the systematic modification of stem cells the more as the feasibility of such an approach has recently been demonstrated with their precursor form (Ref.)