RNA polymerase III-transcribed EBER 1 and 2 transcription units are expressed and hypomethylated in the major Epstein-Barr virus-carrying cell types

The genome of Epstein-Barr virus (EBV) codes for two non-translated small RNA molecules, EBER 1 and 2. We found that both EBERs are expressed in the major EBV-carrying cell types, group I and III Burkitt's lymphoma (BL) cell lines, lymphoblastoid cell lines (LCLs) and in two nude mouse-passaged nasopharyngeal carcinoma (NPC) tumours. The relative amount of EBER 1 and EBER 2 varied in different host cells but did not correlate with the cellular phenotype. The EBER coding and flanking sequences were predominantly hypomethylated at HpaII sites not only in LCLs which usually carry hypomethylated EBV genomes but also in BL and NPC cell lines harbouring EBV episomes that are highly methylated in other regions. Thus, the EBER trancription units, actively transcribed by RNA polymerase III in the major EBV-carrying cell types, represent a methylation-free region in the EBV genome similarly to regulatory sequences of the latent membrane protein gene when the latter is transcribed by RNA polymerase II.