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Abstract

The Epstein-Barr Virus (EBV) is a γ-herpesvirus that establishes a lifelong infection in human hosts. This infection can manifest into cancer. This affliction is attributed to the latent encoded EBV proteins. However, lytic proteins have recently been demonstrated to contribute to tumour development, with notable examples being tegument proteins BNRF1 and BPLF1. In my thesis, I studied BPLF1 in its full form to identify novel regions involved in the EBV life cycle and in carcinogenesis. These goals are achieved through expression in vitro expression studies and in the context of EBV virions that infect primary B cells ex vivo. I used co-immunoprecipitation in tandem with mass spectrometric analysis to identify novel host BPLF1 binding partner SENP6, a deSUMOylase responsible for maintaining genomic integrity. I proceeded to study the effects that BPLF1 has on SENP6 activity and the physiological consequences. I produced domain knockouts of the BPLF1 protein to map the region responsible for interaction and activity of BPLF1 on SENP6. I found that not only does BPLF1 bind to SENP6; it also effectively suppresses SENP6 activity. Downstream effects on SENP6 inhibition are the reduction of Centromeric Protein A (CENP-A) constituency at the centromeres, leading to improper chromosomal segregation during anaphase. This leads to the accumulation of genomic abnormalities such as increased rates of aneuploidy and polyploidy. I found this phenotype occurs independently from the catalytic region of BPLF1 and is mapped to the BPLF1765-1327 stretch of amino acids. B cells exposed to virus particles devoid of BPLF1, showed reduced nuclear abnormalities when compared to virus particles containing BPLF1. I observed increased SUMO2/3 conjugation and loss of CENP-A at the centromeric regions in B cells exposed to virus particles possessing BPLF1 in contrast to virus devoid of BPLF1, showing BPLF1’s interference in chromosomal stability.