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Mitochondrial DNA depletion mediated by herpes simplex virus type 1 UL12.5 Open Access


Other title
mtDNA depletion
Mitochondrial DNA
Mitochondrial localization signal
Mitochondrial localization sequence
Herpes simplex virus type 1
Type of item
Degree grantor
University of Alberta
Author or creator
Duguay, Brett A K
Supervisor and department
Smiley, James (Department of Medical Microbiology and Immunology, University of Alberta)
Examining committee member and department
Hazes, Bart (Department of Medical Microbiology and Immunology, University of Alberta)
Smiley, James (Department of Medical Microbiology and Immunology, University of Alberta)
Burshtyn, Deborah (Department of Medical Microbiology and Immunology, University of Alberta)
Nargang, Frank (Department of Biological Sciences, University of Alberta)
Lippé, Roger (Département de pathologie et biologie cellulaire, Université de Montréal)
Evans, David (Department of Medical Microbiology and Immunology, University of Alberta
Department of Medical Microbiology and Immunology
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Infection with herpes simplex virus type 1 (HSV-1) leads to the rapid and complete loss of mitochondrial DNA (mtDNA) and mitochondrial messenger RNA (mt-mRNA), effectively eliminating gene expression within mitochondria. Previous work determined that a unique 3’ co-terminal transcript arising from within viral alkaline nuclease gene UL12 produced an amino (N)-terminally truncated viral protein, termed UL12.5, which was responsible for mtDNA loss. The UL12 and UL12.5 proteins share the same open reading frame (ORF); however, translation initiation of UL12.5 occurs from the codon equivalent to UL12 M127. The N-terminal truncation of UL12.5 relative to UL12 unmasks a sequence which targets UL12.5 to mitochondria. My working hypothesis stated that UL12.5 localizes to the mitochondrial matrix, in close proximity to mtDNA, to nucleolytically degrade mitochondrial genomes. When I began this research it was clear that UL12.5 caused mtDNA loss by localizing to mitochondria. However, it was unclear how and why UL12.5-mediated mtDNA loss occurred. The data presented in this thesis firstly, support our earlier work and demonstrate that the mitochondrial localization of UL12.5 is controlled by an N-proximal mitochondrial localization sequence (MLS). Furthermore, while this MLS possesses many hallmarks of a mitochondrial matrix targeted protein, UL12.5 does not appear to simply translocate into the mitochondrial matrix. Secondly, inconsistent with the hypothesis, I observed that UL12.5 could cause mtDNA loss in the absence of its inherent nuclease activity, which suggested that cellular nucleases were involved in this process. In support of this revised hypothesis, I discovered that mtDNA loss by UL12.5 was facilitated by the mitochondrial nucleases endonuclease G (ENDOG) and endonuclease G-like 1 (EXOG). Finally, following the construction of a UL12.5-null HSV-1 mutant virus impaired in the ability to cause mtDNA depletion, I observed that the elimination of mtDNA is not required for viral replication. Altogether, the research presented in this thesis support a unique and complex mechanism employed by the HSV-1 UL12.5 protein to destroy mtDNA. These data also leave open the possibility that mtDNA loss may have a significant role in HSV-1 replication in vivo.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Corcoran JA, Saffran HA, Duguay BA, Smiley JR. 2009. Herpes simplex virus UL12.5 targets mitochondria through a mitochondrial localization sequence proximal to the N terminus. J Virol 83:2601-2610.Duguay BA, Smiley JR. 2013. Mitochondrial nucleases ENDOG and EXOG participate in mitochondrial DNA depletion initiated by herpes simplex virus 1 UL12.5. J Virol 87:11787-11797.Duguay BA, Saffran HA, Ponomarev A, Duley SA, Eaton HE, Smiley JR. 2014. Elimination of mitochondrial DNA is not required for herpes simplex virus type 1 replication. J Virol 88:2967-2976.

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