Intracellular forms of adenovirus DNA. III. Integration of the DNA of adenovirus type 2 into host DNA in productively infected cells

KB cells productively infected with human adenovirus type 2 contain an alkali stable class of viral DNA sedimenting in a broad zone between 50 and 90S as compared to 34S for virion DNA. This type of DNA is characterized as viral by DNA DNA hybridization. It is extremely sensitive to shear fragmentation. Extensive control experiments demonstrate that the fast sedimenting viral DNA is not due to artifactual drag of viral DNA mechanically trapped in cellular DNA or to association of viral DNA with protein or RNA. Furthermore, the fast sedimenting DNA is found after infection with multiplicities between 1 and 1,000 PFU/cell and from 6 to 8 hr postinfection until very late in infection (24 hr). Analysis in dye buoyant density gradients eliminates the possibility that the fast sedimenting viral DNA represents supercoiled circular molecules. Upon equilibrium centrifugation in alkaline CsCl density gradients, the fast sedimenting viral DNA bands in a density stratum intermediate between that of cellular and viral DNA. In contrast, the 34S virion DNA isolated and treated in the same manner as the fast sedimenting DNA cobands with viral marker DNA. After ultrasonic treatment of the fast sedimenting viral DNA, it shifts to the density positions of viral DNA and to a lesser extent to that of cellular DNA. Evidence presented demonstrates that the 50 to 90S viral DNA represents adenovirus DNA covalently integrated into cell DNA.