Capsid Assembly and DNA Encapsidation by Epstein-Barr Virus

Epstein-Barr virus (EBV) has two life cycles. After infecting B lymphocytes or epithelial cells, the virus typically remains latent. However, EBV must enter a lytic productive cycle to proliferate and produce infectious particles. During the immediate-early stage of a lytic cycle, the virus firstly expresses two transcription factors, Rta and Zta. These transcription factors activate the genes that express the enzymes that participate in EBV lytic DNA replication. Following EBV DNA replication, the development reaches a late stage, during which EBV capsids are assembled; DNA is encapsidated; tegument proteins are added, and capsids are enveloped. Finally, cells release the EBV particles to begin a new round of EBV infection. Capsid assembly and encapsidation are the most important events in the lytic cycle. So far, only a single gene that encodes the major capsid protein of EBV, BcLF1 has been identified as being involved in capsid assembly. Although sequence analysis has identified several EBV genes that encode proteins with a low degree of sequence identity with proteins involved in capsid assembly and encapsidation of herpes simplex virus type 1 (HSV-1), the functions of these genes have not been verified and many of them involved in these two processes have yet to be identified. This laboratory has created about 10,000 EBV mutants using a shotgun approach. The locations of the mutations in more than 200 mutants have been mapped by DNA sequencing. These mutants will be screened to identify the genes that are involved in EBV capsid assembly and DNA packaging. The proteins involved in capsid assembly will be expressed and the mechanism by which these proteins interact with each other will be biochemically analyzed. Crystallography will also be used to elucidate the way in which the capsid is assembled. With reference to EBV DNA encapsidation, the sequence in the terminal repeats of EBV, which are critical in DNA packaging, will be identified and analyzed. Meanwhile, mutants that cannot package EBV DNA into procapsids will be screened to identify genes that are involved in encapsidation. Proteins that generate a portal for DNA entry, constitute the terminase for DNA processing, and are involved in DNA recombination, will be identified. This investigation will support a better understanding of the development of EBV during the late stage of the lytic cycle. The information may provide a valuable reference for efforts to develop strategies to inhibit the proliferation of EBV.

Project ID:PG9403-1321
External Project ID:NHRI-EX94-9417BI