Plasmid-like replicative intermediates of the Epstein-Barr virus lytic origin of DNA replication.

During the lytic phase of herpesviruses, intermediates of viral DNA replication are found as large concatemeric molecules in the infected cells. It is not known, however, what the early events in viral DNA replication that yield these concatemers are. In an attempt to identify these early steps of DNA replication, replicative intermediates derived from the lytic origin of Epstein-Barr virus, oriLyt, were analyzed. As shown by density shift experiments with bromodeoxyuridine, oriLyt replicated semiconservatively soon after induction of the lytic cycle and oriLyt-containing DNA is amplified to yield monomeric plasmid progeny DNA (besides multimeric forms and high-molecular-weight DNA). A new class of plasmid progeny DNA which have far fewer negative supercoils than do plasmids extracted from uninduced cells is present only in cells undergoing the lytic cycle of Epstein-Barr virus. This finding is consistent with plasmid DNAs having fewer nucleosomes before extraction. The newly replicated plasmid DNAs are dependent on a functional oriLyt in cis and support an efficient marker transfer into Escherichia coli as monomeric plasmids. Multimeric forms of presumably circular progeny DNA of oriLyt, as well as detected recombination events, indicate that oriLyt-mediated DNA replication is biphasic: an early theta-like mode is followed by a complex pattern which could result from rolling-circle DNA replication.