Epstein-Barr virus transcription factors.

Background EBV2 is estimated to infect 90% ofthe world’s population and is by far the best example of a common human virus that efficiently immortalizes human cells. The principal target cells for EBV infection are human B-lymphocytes and oropharyngeal epithelial cells. The virus immortalizes B-lymphocytes and persists in those cells predominantly as a nonproductive, latent infection (reviewed in Ref. 1). Typically, 10-30 copies of the 172-kb circular episomal virus DNA genome are maintained in the nucleus of the latently immortalized B-lymphocyte. The viral DNA is assembled into nucleosomes and replicates once per cell cycle in S phase using the maintenance origin of replication on-P and the virus protein EBNA-1 . Virus gene expression uses mainly the cell polymerase II and Ill transcription apparatus, and virus mRNAs are polyadenylated and spliced like cell mRNAs. EBV also encodes a few transcription regulatory proteins itself, and these are the topic of this review. So far, the virus proteins most clearly shown to be transcription regulatory molecules are EBNA-1 and EBNA-2 in the latent (immortalizing) cycle and BZLF1 and BRLF1 in the virus productive cycle. The location of these genes in the viral genetic map and the nomenclature of EBV genes have been described elsewhere (2, 3).