Characterization of Epstein-Barr virus Type I variants based on linked polymorphism among EBNA3A, -3B, and -3C genes.

Latent Epstein-Barr virus (EBV) nuclear antigens (EBNA)-3A, -3B, and -3C are involved in transcription regulation of both viral and cellular genes. In the present study, we chose functionally important regions within EBNA3A, -3B, and -3C genes with putative tumorigenic potential to investigate natural sequence variations among EBV Type I strains circulating in Europe. Based on the identification of linked EBNA3A, -3B, and -3C sequence patterns, we defined five EBNA3 variants in addition to the B95.8 prototype sequence. Phylogenetic analysis revealed that EBNA3 variant 5, the most diverged from the B95.8 sequence, showed an evolutionary history of intertypic recombination events occurring upstream and downstream of the C-terminus of EBNA3A. The frequency of occurrence of the five newly defined EBNA3 variants was similar for strains causing EBV primary infection or reactivation and was also similar within two of the European areas investigated. In addition, preferential linkages of certain EBNA3 variants to distinct latent membrane protein 1 (LMP1) groups were found to exist. Thus, a combination of more than one polymorphic site in the EBV genome might be involved in determining disease characteristics.