Conservation and progressive methylation of Epstein-Barr viral DNA sequences in transformed cells

Abstract

The structure of intracellular viral DNA from a number of cell lines arising by clonal transformation of human lymphocytes in vitro with Epstein-Barr virus was analyzed. Intracellular viral DNA were partially purified and digested with several restriction endonucleases and the products of digestion were separated by electrophoresis in agarose gels. The viral fragments were detected by transferring the DNA from the gel to nitrocellulose sheets, hybridizing radiolabeled recombinant vectors carrying fragments of viral DNA to those transfers and visualizing the hybrids by autoradiography. These analyses indicated that: regions of repetitious viral DNA do undergo expansion and contraction although 1 size of perdominates; novel sequence arrangements appear in the intracellular viral DNA of different clones but are not found in clones analyzed serially and propagated extensively; the viral DNA is increasingly methylated upon cell propagation. A transformed cell phenotype or a viral phenotype that segregates with the observed progressive methylation was not identified. Analogs of the gross rearrangements of viral DNA observed after lytic infections with high multiplicities of papova-, adeno-, or herpes simplex viruses were not detected in Epstein-Barr viral plasmids.