Replication of plasmids derived from bovine papilloma virus type 1 and Epstein-Barr virus in cells in culture.

The major components encoded by BPV-1 and EBV that act in plasmid replication of these viral DNAs in latently infected cells are now known. The minimal DNA sequences required in cis have been delineated, and the genes whose products are required in trans have been identified. The only required trans-acting gene of EBV, EBNA-1, has been shown to bind specifically to the cis-acting element, oriP. The current advanced understanding of plasmid replication of mtDNA and SV40 DNA is likely to aid in the selection of experiments that will assign functions to these components. In particular, it is exciting to contemplate the possible roles that transcription enhancers and the proteins that bind to these enhancers may perform in plasmid replication. Moreover, one can ask whether or not a virally encoded, site-specific DNA helicase participates in the replication of BPV-1 and EBV plasmids, as it does in SV40 DNA. Continued studies of the regulation of the segregation and the copy-number control of BPV-1 and EBV plasmids are likely to reveal other types of mechanisms, for which our knowledge of mtDNA and SV40 DNA replication does not provide precedents. Findings from these studies may aid not only in our understanding of the regulation of BPV-1 and EBV plasmid replication, but also in the regulation of chromosomal origins of replication.