Topology effect for DNA structure of cisplatin: topological transformation of cisplatin-closed circular DNA adducts by DNA topoisomerase I.

The reaction of cis-Pt(NH3)2Cl2(cis-DDP)-closed circular DNA adducts with DNA topoisomerse I(topo I) were studied by electron microscopy. We identified unique topoisomers such as a singly-linked catenane (2(1)2), trefoil (3(1), and dimetric catenane (2(1)2), etc., by analysis with electron micrographs. These unique recombination products resulted from cis-DDP-intra-twisting looped DNA adducts by DNA topo I, and the products could be explained a new mechanism based on an odd-even number rule. Our results suggest a new model on the working mechanisms for DNA topology of cis-DDP which enhances the recombination of DNA. Based on our results, we propose the topological idea that the yields of a mini closed circular DNA and pseudo trefoil DNA, etc., can be expected by reaction of cis-DDP-DNA-histone complexes with DNA topo I in the body.