Biochemistry of latent Epstein-Barr virus infection and associated cell growth transformation

Abstract

There is sufficient knowledge of the biochemistry of Epstein-Barr virus (EBV) persistence and gene expression in latent growth-transforming infection and of the persistence and expression of other oncogenic viruses to permit interesting and possibly useful comparisons. Most smaller oncogenic viral genomes usually persist solely as integrated DNAs despite their ability to circularize. Papilloma and hepatitis viruses may persist as episomes, and parts of their genomes may integrate. Usually, only the oncogenic fragment of adenovirus DNA is integrated into cell DNA. In contrast, the entire EBV genome persists in cells as an episome or as integrated DNA. Thus, EBV may have novel mechanisms to maintain its complete genome as an episome or as a complete integrated virus DNA. Three viral genes are expressed in latently EBV-infected growth-transformed cells, each of which encodes one RNA and one protein. Two of the proteins are probably nuclear DNA-binding proteins; the third is probably a membrane protein. Thus, the repertoire of genes expressed is similar in complexity and intracellular distribution to that expressed by papova and adenoviruses in cellular transformation. The papova and adenovirus-transforming genes are partially analogous to retrovirus oncogenes. This similarity cannot as yet be extended to EBV. There is no homology at the DNA-sequence or protein-sequence level between EBV and other viral or cell oncogenes. Thus, it remains important to pursue analysis of the EBV-transforming genes. Identification of these genes is a first step in discerning their function in latent growth-transforming cell infection. Parts of each of these genes are being made in bacteria. The bacterial products enable us to make antisera that are specific for each of the viral proteins. These antisera can also be used to identify the viral proteins within latently infected growth-transformed cells or within cells stably expressing transfected virus genes. The antisera can also be used to study the association of Epstein-Barr nuclear antigen (EBNA) 1 and 2 with DNA and of the lymphocyte-determined membrane antigen (LYDMA) with the cell membrane. The three genes must be introduced into nontransformed cells to determine whether, alone or in combination, they are sufficient to accomplish cell growth transformation.