The Epstein-Barr virus (EBV)BamHI

Dengue virus type 2, a member of the family Flaviviridae, encodes a single polyprotein precursor consisting of 3391 amino acids residues that is processed to at least 10 mature proteins by host and viral proteases. The NS3 protein contains a domain commonly found in cellular serine proteinases that in cooperation with NS2B is involved in polyprotein processing. In addition, NS3 and NS5 proteins contain conserved motifs found in several RNA helicases and RNA-dependent RNA polymerases, respectively. Both enzymatic activities have been suggested to be involved in viral RNA replication. In this report, we demonstrate that the NS3 and NS5 proteins interact in vivo in dengue virus type 2-infected monkey kidney (CV-1) cells and in HeLa cells coinfected with recombinant vaccinia viruses encoding these proteins as shown by coimmunoprecipitations and immunoblotting methods. We also show by immunofluorescence, metabolic labeling, and two-dimensional peptide mapping that NS5 is a nuclear phosphoprotein and that phosphorylation occurs on serine residues at multiple sites. Furthermore, NS5 exists in differentially phosphorylated states in the nuclear and the cytoplasmic fractions, and only the cytoplasmic form of NS5 is found to coimmunoprecipitate with NS3, suggesting that differential phosphorylation may control the interaction between these proteins and its function in the viral RNA replicase.

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The biologic hallmark of Epstein-Barr virus (EBV) and its usual interaction with B lymphocytes is latency. Several types of latency with distinct patterns of viral gene expression have been described. Type I latency is exemplified by Burkitt's lymphomas (BL) in vivo and earlier passages of cultured cell lines derived from BL tissues. EBV nuclear antigen 1 (EBNA-1), and in some cases latent membrane protein 2A (LMP-2A), is expressed in this form of latency (7,35,36,41,59). Several reports suggest that a type I-like form of latency exists in healthy carriers of EBV (7,35,36,41,59). Interestingly, cells in type I latency can escape host immune surveillance because EBNA-1 can interfere with its peptide presentation on major histocompatibility complex class I molecules (29), which might explain the lifelong reservoir of virus in immunocompetent, seropositive persons. Type III latency is represented by lymphoblastoid cell lines established after EBV infection of adult primary B cells in vitro, by some BL lines, and in B-cell lymphomas in immunodeficient states. Nine viral proteins, including six nuclear proteins (EBNA-1, EBNA-2, EBNA-3A, EBNA-3B, EBNA-3C, and EBNA-LP) and three integral membrane proteins (LMP-1, LMP-2A, and LMP-2B), are expressed. In addition, in all three forms of latency, EBV-encoded RNAs (EBERs) are expressed (reviewed in references 25 and 43).EBNA-1 is the sole viral protein needed for the replication of the EBV episome and maintenance of the latent infection state; both events are essential for cell immortalization (reviewed in references 25 and 43). The promoter usage for expression of EBNA-1 differs in different types of latency. In type I latency, the BamHI Q promoter (Qp) is used for the transcription of EBNA-1 mRNA. However, in type III latency, Qp is silent, and the BamHI C and/or BamHI W promoters (C/ Wp) are used. The biological consequence of the Qp-to-C/Wp switch and the conversion to type III latency is the expression of the full spectrum of latency genes (reviewed in references 25 and 43), which confers enhanced cell survival, growth, and invasive potential (8,17,19,22,53,60,65).Since Qp usage not only relates to the survival of the virus in an immunocompetent host but also is associated with several tumors, dissecting the regulation of Qp is essential for understanding the viral program in EBV-associated malignancies. The functional importance of Qp for the EBV life cycle is underscored by the facts that all EBV-positive tumor specimens collected from Africa, North America, and Asia have conserved Qp sequence (58) and that conserved structural and functional cis elements (e.g., an interferon [IFN]-stimulated response element [ISRE] and the Q locus [see Fig. 4A]) also exist in the Old World primate lymphocryptoviruses, which are simian EBVs (47). Both EBNA-1 and host factors are involved in the transcriptional regulation of Qp. The downstream element of Qp, the Q locus (Fig. 4A), contains two binding sites for the EBNA-1 protein, which binds to and acts in an autoregulatory manner to...

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Interferon (IFN) regulatory factors (IRF) are a family of transcription factors with multiple functions. IRF-7 was initially cloned within the biologic context of Epstein-Barr virus (EBV) latency and discovered to have an intimate relation with the EBV primary oncogenic protein, latent membrane protein-1 (LMP-1). EBV regulates and uses IRF-7 as a secondary mediator for several target genes involved in latency and immune regulation. Other than its functions in EBV latency, IRF-7 has been identified as one of the major players in virally induced IFN production that is central to innate immunity. Thus, IRF-7 plays important roles in a variety of biologic systems.

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Epstein-Barr virus (EBV) latent membrane protein 1 (LMP-1