Covalently closed circular forms of viral DNA are found in the nuclei of cells acutely infected by avian sarcoma virus. In this report we show that dimeric and trimeric forms of closed circular DNA are present, in addition to the previously characterized, predominant monomeric species. The identities of these oligomeric circular molecules were verified by their characteristic behavior during equilibrium centrifugation in cesium chloride-propidium diiodide gradients, rate-zonal centrifugation in sucrose gradients, and electrophoresis in agarose gels, before and after digestion with nucleases. Restriction endonuclease cleavage of isolated dimeric and trimeric molecules indicates that they consist of monomers linked in a "head-to-tail" orientation.
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