title: Epstein-Barr virus polymerase processivity factor enhances BALF2 promoter transcription as a coactivator for the BZLF1 immediate-early protein.
abstract: The Epstein-Barr virus (EBV) BMRF1 protein is an essential replication protein acting at viral replication forks as a viral DNA polymerase processivity factor, whereas the BALF2 protein is a single-stranded DNA-binding protein that also acts at replication forks and is most abundantly expressed during viral productive replication. Here we document that the BMRF1 protein evidently enhances viral BZLF1 transcription factor-mediated transactivation of the BALF2 gene promoter. Mutagenesis and electrophoretic mobility shift assays demonstrated the BALF2 promoter to harbor two BZLF1 protein-binding sites (BZLF1-responsive elements). Direct binding of the BZLF1 protein to BZLF1-responsive elements and physical interaction between BZLF1 and BMRF1 proteins are prerequisite for the BMRF1 protein up-regulation of the BALF2 gene promoter. A monomeric mutant, C95E, which is defective in homodimerization, could still interact and enhance BZLF1-mediated transactivation. Furthermore although EBV protein kinase phosphorylates BMRF1 protein extensively, it turned out that phosphorylation of the protein by the kinase is inhibitory to the enhancement of the BZLF1-mediated transactivation of BALF2 promoter. Exogenous expression of BMRF1 protein augmented BALF2 expression in HEK293 cells harboring the EBV genome but lacking BMRF1 and BALF5 genes, demonstrating functions as a transcriptional regulator in the context of viral infection. Overall the BMRF1 protein is a multifunctional protein that cannot only act as a DNA polymerase processivity factor but also enhances BALF2 promoter transcription as a coactivator for the BZLF1 protein, regulating the expression level of viral single-stranded DNA-binding protein.
authors.affiliation: Division of Virology, Aichi Cancer Center Research Institute, Chikusa-ku, Nagoya 464-8681, Japan.
authors.forename: Sanae
authors.initials: S
authors.lastname: Nakayama
authors.forename: Takayuki
authors.initials: T
authors.lastname: Murata
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Murayama
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Yasui
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Sato
authors.forename: Ayumi
authors.initials: A
authors.lastname: Kudoh
authors.forename: Satoko
authors.initials: S
authors.lastname: Iwahori
authors.forename: Hiroki
authors.initials: H
authors.lastname: Isomura
authors.forename: Teru
authors.initials: T
authors.lastname: Kanda
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Tsurumi
mesh_terms: D000956:Antigens, Viral / Q000378:metabolism*; D001483:Base Sequence; D001667:Binding, Competitive; D045744:Cell Line, Tumor; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D015967:Gene Expression Regulation, Viral; D004854:Herpesvirus 4, Human / Q000378:metabolism*; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000737:chemistry; D015534:Trans-Activators / Q000378:metabolism; D014764:Viral Proteins / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D000956:Antigens, Viral; C096364:BALF2 protein, Human herpesvirus 4; C063676:BZLF1 protein, Herpesvirus 4, Human; D004268:DNA-Binding Proteins; C083204:Epstein-Barr virus early antigen diffuse component; D011994:Recombinant Proteins; D015534:Trans-Activators; D014764:Viral Proteins; D008156:Luciferases