A dual-circular plasmid structure dependent on DNA replication generated in monkey COS7 cells and cell extracts

When monkey COS7 cells are transfected with plasmids pSVod or pSV2-neo, a DNA structure can be detected consisting of two circular forms linked by a duplex bridge. Generation of this structure is enhanced by camptothecin, an inhibitor of DNA topoisomerase I. Generation of dual-circles in vitro, using a DNA replication system with added T-antigen, requires template DNA with an SV40 origin. Heterogeneous dual-circles can be visualized involving two initially independent molecules of different size. Implications for in vitro studies of certain types of recombination are discussed.