In vitro formation of multimeric DNA structures mediated by purified simian virus 40 chromatin.

Simian virus 40 chromatin was incubated after purification by sucrose density-gradient centrifugation with various circular double-stranded DNA substrates. Monomeric rings were converted in the presence of Mg2+ to structures possessing a higher degree of complexity. Dimeric catenanes, as well as multimeric linear structures and concatemers, were generated, indicating that recombination events had occurred in vitro involving covalent linkage between different DNA molecules. Furthermore, apparently fused dimeric rings were observed. Their structures suggest that they may be recombination intermediates such as those described in a prokaryotic system [Potter, H. & Dressler, D. (1976) Proc. Natl. Acad. Sci. USA 73, 3000-3004]. Recombination did not take place between heterologous DNA substrates, as exclusively homologous multimeric DNA structures were observed.