Evidence for integrated EBV genomes in Raji cellular DNA.

Human lymphoid cell lines cannot be grown in long-term tissue culture, as a rule, unless the cells have been transformed by Epstein-Barr virus (EBV). The latent EBV DNA in established cell lines, is mainly present as free covalently closed circles but viral DNA sequences with properties of integrated DNA also seem to be present. We have extended the studies on the physical state of the EB viral DNA sequences in the cell line Raji which appear at a lower density than that for free EB viral DNA during fractionation on CsCl density gradients. In such material a novel EcoRI EBV DNA fragment is present, which hybridizes to viral sequences homologous to EcoRI A. This fragment is not present in free covalently closed circular EBV DNA. When this EcoRI fragment is further analysed with HindIII a smaller fragment than expected, which contains BamHI W sequences, is detected. The demonstration of this HindIII fragment and its characteristics as a joint, viral-host chromosome fragment will be discussed.