Investigating the Ubiquitin-proteasome System during Poxvirus Infection

Abstract

Ubiquitylation is a post-translated modification that is important for the host immune response to virus infection. Concurrently, it is also exploited by poxviruses for viral replication and evasion of the host immune response. Thus, this project focused on further elucidating how the ubiquitin (Ub) system is engaged during poxvirus infection. p28, a poxvirus encoded E3 Ub-ligase, is a virulence factor of ectromelia virus (ECTV) in susceptible strain A mice. To further investigate p28 function, we completely deleted the p28 gene from ECTV (ECTV-Δp28). The ECTV-Δp28 virus exhibited severely impaired virus production and genome replication in a mouse strain, cell type, and multiplicity of infection-dependent manner. Moreover, a FLAG-tagged p28 protein with a fusion Ub moiety was expressed and developed as a tool to capture p28 potential substrate proteins. To determine the DNA binding properties of p28, I purified recombinant His-tagged p28 and examined the interaction between p28 and poxvirus hairpin DNA. To get a more comprehensive understanding of how proteins are ubiquitylated early after vaccinia virus (VACV) infection, a proteomics approach was used to identify and quantify ubiquitylated peptides in cells with or without VACV infection. These included peptides associated with TRIM25, a cellular E3 Ub/ ISG15-ligase, whose ubiquitylation is induced by a gene(s) in either arm of the VACV genome. Taken together, this thesis has revealed novel information about how poxviruses manipulate ubiquitylation.