Analysis of the Epstein-Barr virus transcription factor, Zta

Balan, Nicolae (2014) Analysis of the Epstein-Barr virus transcription factor, Zta. Doctoral thesis (PhD), University of Sussex.

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Epstein-Barr virus (EBV) is a ubiquitous pathogen that infects most of the adult population and persists for life after the initial contact. The extreme success of the virus is attributed to its bipartite life cycle, which consists of a dormant-like state of latency, with periodical reactivation to the virus producing, lytic phase. Zta (BZLF1, Z, Zebra or EB1) is a multifunctional viral protein that belongs to the bZIP family of transcription factors and is known as the master lytic regulator of EBV. Together with transcriptional activation, Zta has been shown to be involved in DNA binding-dependent transcriptional repression, particularly of the host class II major histocompatibility complex transactivator, CIITA. Distinct protein domains, as well as various post translational modifications, like phosphorylation of Serine 209 by the viral protein kinase (VPK), have been linked to different functional roles of Zta.
In the present study, it was shown that VPK can partially inhibit SUMOylation of Zta on Lysine 12, in a manner which was not dependent on Serine 209 phosphorylation. However, no direct interaction of VPK and Zta could be observed and no significant effect of either proteins on histone H2AX phosphorylation was seen.
Interestingly, in vitro reporter assays revealed that fusion of a SUMO moiety to the amine-terminus of Zta inhibited repression of the CIITA promoter, but not the activation of the viral BHLF1 promoter, pointing at divergent mechanisms of action of transcriptional repression and activation by Zta. Moreover, truncation of the carboxy-terminal dimerisation domain of Zta (crucial for protein-DNA interaction) abrogated BHLF1 transactivation but not CIITA down-regulation, revealing underlying diffe rences in DNA binding requirements for the two processes.
Further in silico sequence analysis, coupled with a mutation approach of the CIITA promoter, confirmed that an alternate route to the Zta DNA binding-dependent repression exists. Finally, no single promoter element could be linked to down-regulation of CIITA, suggesting sequestration of a possible, yet unknown cofactor, by Zta.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Biochemistry
Subjects: Q Science > QD Chemistry > QD0241 Organic chemistry > QD0415 Biochemistry
Depositing User: Library Cataloguing
Date Deposited: 17 Jun 2014 14:50
Last Modified: 05 Jul 2016 08:54

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