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

  • Author / Creator
    Duguay, Brett A K
  • 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.

  • Subjects / Keywords
  • Graduation date
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
    • Department of Medical Microbiology and Immunology
  • Specialization
    • Virology
  • Supervisor / co-supervisor and their department(s)
    • Smiley, James (Department of Medical Microbiology and Immunology, University of Alberta)
  • Examining committee members and their departments
    • Hazes, Bart (Department of Medical Microbiology and Immunology, University of Alberta)
    • Burshtyn, Deborah (Department of Medical Microbiology and Immunology, 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
    • Nargang, Frank (Department of Biological Sciences, University of Alberta)
    • Smiley, James (Department of Medical Microbiology and Immunology, University of Alberta)