Identification of a rare Epstein-Barr virus variant that enhances early antigen expression in Raji cells

Early antigens (EAs) are made when the P3J-HR-1 strain of Epstein-Barr virus (EBV) infects cells that already harbor latent EB viral genomes. We wished to identify EBV genes that might participate in induction of EAs. We have recently isolated from the HR-1 line EB viral variants that are unable to induce EAs. We have now isolated a clone of HR-1 cells that releases virus with the capacity to induce EA. We compared the genome of the EB variant that possesses the capacity to induce EA with that of a variant that is unable to induce EA and with parental stock that was the source of both different biotypes of EBV. The variant that is able to induce EA contains, in molar or greater quantities, additional fragments of EBV DNA not found in the variant that lacks that capacity. These same DNA fragments are present in submolar quantities in the parental DNA, indicating that they represent a subpopulation in the parental viral DNA mixture. We thus provide evidence that EA induction is brought about by unusual forms of EBV DNA that are likely to act by regulating expression of the genome.