| Summary: | 碩士 === 國立中央大學 === 生命科學系 === 106 === Baculovirus is widely used as a tool for the expression of eukaryotic proteins and as a carrier for the delivery of foreign genes into cells. The infection cycle can be considered to occur into three stages: early, late, and very late phases. The viral early genes should be responsible for proper viral infections and control subsequent viral gene expression and propagation. The product of the immediately early gene-2 (ie2) is a strong trans-activator for gene expression in insect Sf21 and mammalian Vero E6 cells. It is known that host death domain associated protein (Daxx) and Histone H3.3 can bind and strongly block the function of the intruding viral DNA, unexpectedly, this study found that IE2 could interact with Daxx and H3.3 to locate viral DNA. Further studies showed that IE1 targets IE2 through the help of other viral factors, because IE1 and IE2 do not co-localize by plasmids containing ie1 and ie2 genes, rather co-localization only occurs upon virus infection. In order to identify the viral genes responsible for IE1 and IE2 co-localization, a set of overlapping cosmid clones covering the entire 134-kb AcMNPV genome were co-transfected collectively and separately with IE1 and IE2. We found that the Bgl-II-B fragment of the viral genome may contain the element(s) to affect IE1/IE2 co-localization. Therefore, upon initial baculovirus infection, IE2 can target Daxx to approach viral DNA. After targeting to viral DNA, IE2 helps to remove Daxx, and IE1 in turn targets viral DNA indirectly though IE2. Then IE1 further triggers IE2 self-degradation through ubiquitination pathway to create an environment suitable for DNA replication. Thus, this study delineates a complex story regarding how viral factors overcome host immune restriction, and manage to target their DNA for further gene expression and DNA replication.
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