Effect of phosphorylation on the transactivation activity of Epstein-Barr virus BMRF1, a major target of the viral BGLF4 kinase.
Modification of human herpesvirus DNA polymerase processivity factors (PFs) by phosphorylation occurs frequently during viral lytic replication. However, functional regulation of the herpesvirus PFs through phosphorylation is not well understood. In addition to processivity, the PF BMRF1 of Epstein-Barr virus can function as a transactivator to activate the BHLF1 promoter within the lytic origin of replication (oriLyt), which is assumed to facilitate DNA replication through remodelling viral chromatin structure. BMRF1 is known to be phosphorylated by the viral BGLF4 kinase, but its impact on BMRF1 function is unclear. Seven candidate BGLF4 target sites were predicted within a proline-rich region between the DNA-processivity and nuclear-localization domains of BMRF1. We show that four of these residues, Ser-337, Thr-344, Ser-349 and Thr-355, are responsible for the BGLF4-induced hyperphosphorylation of BMRF1. In functional analyses, a phosphorylation-mimicking mutant of BMRF1 shows similar nuclear localization, as well as DNA-binding ability, to the wild type; however, it displays stronger synergistic activation of the BHLF1 promoter with Zta. Notably, BGLF4 downregulates BMRF1 transactivation and enhances the transactivation activity of Zta and the synergistic activation of BMRF1 and Zta on the BHLF1 promoter. Our findings suggest that BGLF4 may modulate the activation of the oriLyt BHLF1 promoter coordinately through multiple mechanisms to facilitate optimal oriLyt-dependent viral DNA replication.
Yang
Pei-Wen
PW
Graduate Institute and Department of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan, ROC.
Chang
Shih-Shin
SS
Graduate Institute and Department of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan, ROC.
Tsai
Ching-Hwa
CH
Graduate Institute and Department of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan, ROC.
Chao
Yi-Hsin
YH
Graduate Institute and Department of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan, ROC.
Chen
Mei-Ru
MR
Graduate Institute and Department of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan, ROC.
D000595:Amino Acid Sequence; D000956:Antigens, Viral / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004261:DNA Replication; D004279:DNA, Viral / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D004854:Herpesvirus 4, Human / Q000502:physiology*; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000235:genetics; D018741:Replication Origin; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*; D014779:Virus Replication
D000956:Antigens, Viral; C063676:BZLF1 protein, Herpesvirus 4, Human; D004279:DNA, Viral; D004268:DNA-Binding Proteins; C083204:Epstein-Barr virus early antigen diffuse component; D015534:Trans-Activators; D014764:Viral Proteins; C406063:BGLF4 protein, Epstein-Barr virus; D017346:Protein Serine-Threonine Kinases