Dimer-size DNA circles in a leukemic cell immortalized with the Epstein-Barr virus

The intracellular state of the 30 viral genome equivalents of Epstein-Barr virus (EBV) DNA carried in latent form by the CII cell line, established from a chronic lymphocytic leukemia patient, has been partially characterized. The CII line, which has markers confirming its tumor origin, extends the analysis of the intracellular state of EBV DNA to include other, non-Burkitt lymphoid tumor cells. Monomer-size, free, circular EBV genomes, the major intracellular viral DNA species in other EBV-transformed cells, were absent or present in only minor amounts. Instead, EBV DNA sequences were found associated with a circular DNA form twice the size of the 110 x 10(6) Mr EBV genome. Though circular dimers of mtDNA have been found exclusively in human leukemic lymphocytes, the CII line is similar to normal cells in having only monomer-size mtDNA molecules, which can occur either singly or as catenated forms of two or more interlocking 5-micrometer mtDNA circles.