A concatenated form of Epstein-Barr viral DNA in lymphoblastoid cell lines induced by transfection with BZLF1.

The replicative form of Epstein-Barr virus (EBV) DNA was studied using two lymphoblastoid cell lines, X50-7 and 6F11, which are latently infected by Epstein-Barr virus. The lytic cycle of EBV infection was induced by transfection of the cells with the BRLF1/BZLF1 coding region of the P3HR-1 defective genome. We combined two techniques to identify the productive replicative form of Epstein-Barr viral DNA in the lytic cycle-induced cells. Restriction enzyme analysis followed by Southern blot hybridization identified a significant increase in the fused fragment encompassing both ends of EBV DNA. This indicates an increase in either episomal DNA or concatameric linear DNA. Southern blot analysis of in situ lysing gels revealed that the cellular content of linear EBV DNA was also increased significantly after the initiation of the viral lytic cycle, while the amount of circular DNA remained approximately constant. We propose from these results that the source of the fused fragment encompassing both ends of EBV DNA is a concatenated linear EBV DNA molecule, and that such a concatenated molecule most likely represents a replicative form of EBV DNA in productively infected cells.