Beata Cohan, University of Toronto

Beata Cohan, Samuel G. Salamun, Lori Frappier. Department of Molecular Genetics, University of Toronto

Expressing & Multiplying

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus that infects ~90% of humans, and is causatively associated with infectious mononucleosis, multiple malignancies and multiple sclerosis. EBV alternates between latent and lytic infectious cycles, the latter of which involves expression of ~70 proteins leading to viral genome amplification at nuclear replication centers and virion production. The BMRF1 lytic protein localizes to replication centers and serves an essential role as the processivity factor for the viral DNA polymerase. BMRF1 also has an additional role in activating the transcription of some EBV late genes. Through affinity-purification coupled to mass spectrometry, we determined that BMRF1 interacts with the cellular NuRD (nucleosome remodelling and deacetylation) complex, which affects cellular gene expression and DNA repair through chromatin modifications. We showed that BMRF1 binds the MTA2 and RBBP4 NuRD subunits through a consensus motif, and that point mutation of this motif in BMRF1 (RK mutant) abrogates NuRD binding and transcriptional activation by BMRF1 (2019 J Virol.93:e01070). In addition, NuRD subunits co-localize with BMRF1 at viral replication centers, prompting us to investigate the importance of NuRD in EBV DNA amplification. Silencing of NuRD subunits, decreased EBV genome amplification and impaired late gene expression. Additionally, studies comparing EBV virus containing the BMRF1 RK mutation to WT virus showed that NuRD localization to replication centers and lytic genome amplification are both significantly reduced. The results indicate that BMRF1 recruits NuRD to EBV replication centres, where it contributes to viral genome amplification and transcriptional activation, likely through its chromatin remodelling effects.