Epstein-Barr virus polymerase processivity factor enhances BALF2 promoter transcription as a coactivator for the BZLF1 immediate-early protein.
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.
Nakayama
Sanae
S
Division of Virology, Aichi Cancer Center Research Institute, Chikusa-ku, Nagoya 464-8681, Japan.
Murata
Takayuki
T
Murayama
Kazutaka
K
Yasui
Yoshihiro
Y
Sato
Yoshitaka
Y
Kudoh
Ayumi
A
Iwahori
Satoko
S
Isomura
Hiroki
H
Kanda
Teru
T
Tsurumi
Tatsuya
T
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
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