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Crystal structure of epstein-barr virus DNA polymerase processivity factor BMRF1.

ABSTRACT: The DNA polymerase processivity factor of the Epstein-Barr virus, BMRF1, associates with the polymerase catalytic subunit, BALF5, to enhance the polymerase processivity and exonuclease activities of the holoenzyme. In this study, the crystal structure of C-terminally truncated BMRF1 (BMRF1-DeltaC) was solved in an oligomeric state. The molecular structure of BMRF1-DeltaC shares structural similarity with other processivity factors, such as herpes simplex virus UL42, cytomegalovirus UL44, and human proliferating cell nuclear antigen. However, the oligomerization architectures of these proteins range from a monomer to a trimer. PAGE and mutational analyses indicated that BMRF1-DeltaC, like UL44, forms a C-shaped head-to-head dimer. DNA binding assays suggested that basic amino acid residues on the concave surface of the C-shaped dimer play an important role in interactions with DNA. The C95E mutant, which disrupts dimer formation, lacked DNA binding activity, indicating that dimer formation is required for DNA binding. These characteristics are similar to those of another dimeric viral processivity factor, UL44. Although the R87E and H141F mutants of BMRF1-DeltaC exhibited dramatically reduced polymerase processivity, they were still able to bind DNA and to dimerize. These amino acid residues are located near the dimer interface, suggesting that BMRF1-DeltaC associates with the catalytic subunit BALF5 around the dimer interface. Consequently, the monomeric form of BMRF1-DeltaC probably binds to BALF5, because the steric consequences would prevent the maintenance of the dimeric form. A distinctive feature of BMRF1-DeltaC is that the dimeric and monomeric forms might be utilized for the DNA binding and replication processes, respectively.

SUBMITTER: Murayama K

PROVIDER: S-EPMC2791018 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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Crystal structure of epstein-barr virus DNA polymerase processivity factor BMRF1.

Murayama Kazutaka K Nakayama Sanae S Kato-Murayama Miyuki M Akasaka Ryogo R Ohbayashi Naomi N Kamewari-Hayami Yuki Y Terada Takaho T Shirouzu Mikako M Tsurumi Tatsuya T Yokoyama Shigeyuki S

The Journal of biological chemistry 20091201 51

The DNA polymerase processivity factor of the Epstein-Barr virus, BMRF1, associates with the polymerase catalytic subunit, BALF5, to enhance the polymerase processivity and exonuclease activities of the holoenzyme. In this study, the crystal structure of C-terminally truncated BMRF1 (BMRF1-DeltaC) was solved in an oligomeric state. The molecular structure of BMRF1-DeltaC shares structural similarity with other processivity factors, such as herpes simplex virus UL42, cytomegalovirus UL44, and hum ...[more]

PMID: 19801550

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Project description:During the lytic phase of Epstein-Barr virus (EBV), binding of the transactivator Zta to the origin of lytic replication (oriLyt) and the BHLF1 transcript, forming a stable RNA-DNA hybrid, is required to initiate viral DNA replication. EBV-encoded viral DNA replication proteins form complexes to amplify viral DNA. BMRF1, the viral DNA polymerase accessory factor, is essential for lytic DNA replication and also known as a transcriptional regulator of the expression of BHLF1 and BALF2 (single-stranded DNA [ssDNA]-binding protein). In order to determine systematically how BMRF1 regulates viral transcription, a BMRF1 knockout bacmid was generated to analyze viral gene expression using a viral DNA microarray. We found that a subset of Rta-responsive late genes, including BcLF1, BLLF1, BLLF2, and BDLF3, were downregulated in cells harboring a BMRF1 knockout EBV bacmid (p2089ΔBMRF1). In reporter assays, BMRF1 appears to transactivate a subset of viral late promoters through distinct pathways. BMRF1 activates the BDLF3 promoter in an SP1-dependent manner. Notably, BMRF1 associates with the transcriptional regulator BRG1 in EBV-reactivated cells. BMRF1-mediated transactivation activities on the BcLF1 and BLLF1 promoters were attenuated by knockdown of BRG1. In BRG1-depleted EBV-reactivated cells, BcLF1 and BLLF1 transcripts were reduced in number, resulting in reduced virion secretion. BMRF1 and BRG1 bound to the adjacent upstream regions of the BcLF1 and BLLF1 promoters, and depletion of BRG1 attenuated the recruitment of BMRF1 onto both promoters, suggesting that BRG1 is involved in BMRF1-mediated regulation of these two genes. Overall, we reveal a novel pathway by which BMRF1 can regulate viral promoters through interaction with BRG1.IMPORTANCE The cascade of viral gene expression during Epstein-Barr virus (EBV) replication is exquisitely regulated by the coordination of the viral DNA replication machinery and cellular factors. Upon lytic replication, the EBV immediate early proteins Zta and Rta turn on the expression of early proteins that assemble into viral DNA replication complexes. The DNA polymerase accessory factor, BMRF1, also is known to transactivate early gene expression through its interaction with SP1 or Zta on specific promoters. Through a global analysis, we demonstrate that BMRF1 also turns on a subset of Rta-regulated, late structural gene promoters. Searching for BMRF1-interacting cellular partners revealed that the SWI/SNF chromatin modifier BRG1 contributes to BMRF1-mediated transactivation of a subset of late promoters through protein-protein interaction and viral chromatin binding. Our findings indicate that BMRF1 regulates the expression of more viral genes than thought previously through distinct viral DNA replication-independent mechanisms.

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Crystal structure of epstein-barr virus DNA polymerase processivity factor BMRF1.

Publications

Crystal structure of epstein-barr virus DNA polymerase processivity factor BMRF1.

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