Marked variation in the size of genomic plasmids among members of a family of related Epstein-Barr viruses.

Epstein-Barr virus (EBV) genomes in the P3J-HR-1 (HR-1) Burkitt lymphoma cell line rearrange at a high rate. Previously described deletions and rearrangements in HR-1 cells have been found at sites of EBV replication in vivo, suggesting that DNA rearrangement may be an integral aspect of EBV biology and pathogenesis. We examined the structure of linear EBV genomes in subcultures of HR-1 cells using contour-clamped homogenous electric field gel electrophoresis. We developed a second pulsed electrophoretic technique to separate intracellular circular EBV plasmids. The standard, linear HR-1 EBV genome was approximately 155 kilobases in length. Linear molecules of less than unit length, presumably defective genomes, were seen in numerous subcultures. Linear intracellular genomes greater than 155 kilobases were also detected, but only linear genomes of 155 kilobases or less were packaged into virions. The size of circular EBV plasmids also varied greatly among HR-1 subcultures, some of which contained two plasmids of different size. The progeny of the unusual circular plasmids could be either standard or nonstandard linear genomes. No aberrant linear or circular form was detected in a subculture carrying the previously described het fragments. Pulsed-gel electrophoresis has provided two additional characteristics of mutant EBVs: abnormal linear and circular genome configurations.