The structure of the termini of the DNA of Epstein-Barr virus

Abstract

We have studied the DNA of Epstein-Barr virus (EBV) isolated from the B95-8 strain of that virus ( Miller and Lipman, 1973). When EBV DNA is partially digested with λ-exonuclease and allowed to reanneal, up to 50% of the full-length molecules circularize. The arrangements of nucleotide sequences containing the terminal repeats identified in this circularization experiment have been determined. Those fragments of viral DNA generated by digestion with restriction endonucleases which are terminal and contain the terminal repeats have been identified by their sensitivity to digestion of full-length DNA by λ-exonuclease and by virtue of their being partially homologous to one another. The population of DNA molecules in the B95-8 strain of EBV was found to be nonuniform. The nonuniformity results from different molecules having different numbers of a 0.37 megadalton terminal repeat at each end. About 70% of molecules have four terminal repeats at one end, while four equal classes, each comprising approximately 25% of the population, have one, two, three or four repeats at the other end. The arrangements of nucleotide sequences identified as being terminal in virion DNA were studied in the intracellular circular viral DNA of cells transformed by a single particle on EBV. All fragments produced by digestion with endonucleases and scored as being terminal in virion DNA were absent from intracellular circular DNA. An additional fragment was identified in the digests of intracellular DNA of each transformed clone. The molecular weights of the new fragments equal the sum of the molecular weights of two terminal fragments which are joined upon intracellular circularization of viral DNA.