PhD Defence: Weijia Zhang

Opponents:
Professor Roger A. Garrett (chair), Department of Biology, University of Copenhagen, Denmark. Associate Professor Gisle Alberg Vestergaard, Department of Health Technology, DTU, Denmark.
Professor Qunxin She, Microbial Technology Institute, Shandong University, Qingdao, P. R. China.

Supervisor:
Associate Professor Xu Peng, Department of Biology, University of Copenhagen, Denmark.

Abstract
The replication initiator protein (Rep) is one of the essential proteins of rolling circle replication among phages and circular plasmids. Previous in vitro studies showed that Rep of an archaeal virus can cleave the terminal sequence on one strand to initiate the replication. In this study, we further characterized the Rep protein by in vivo study. The rep gene was knocked out from SIRV2 genome, causing a decrease of virus yield by 4-6 fold. The absence of Rep abolished replication initiation at the genomic termini of SIRV2, indicating its role initiating replication from the genomic end region. When the infection was performed in the presence of CRISPR and Acrs, the loss of Rep caused a more significant drop of viral yield by 50-180 fold. Co-infection of Sulfolobus host with a mixture of the mutant virus and the parental virus (with Rep) at a ratio of 10:1 revealed that the mutant virus was eventually outcompeted by the parental virus. These results suggest the Rep protein provide selective advantage in virus-virus conflicts during the CRISPR-Acrs warfare.

The spindle-shaped archaeal virus SMV1 is an ideal candidate as nanoplatform for applications such as gene therapy. To package modified genetic elements into the empty capsid of SMV1, it is important to understand the pathway of virus particle assembly. The preliminary results in this thesis showed protein interactions between gp32, a virion protein of unknown function and two major coat proteins. The in vitro assembly of virion proteins revealed irregular structures of sizes (around 100nm) smaller than normal SMV1 virions (around 200nm), which is probably due to incomplete protein interactions.

A version of the PhD thesis is available with the PhD secretary

Digital platform: https://ucph-ku.zoom.us/j/7858897310