| Summary: | 碩士 === 國立臺灣大學 === 生化科技學系 === 106 === Epstein-Barr virus (EBV) is a human herpesvirus, which infects more than 90% of the population. After infection, EBV immortalizes its host cells, establishing latent infection. Although the infection is usually asympotmatic, latent EBV infection is often associated with human cancers. The virus can be reactivated by specific environmental changes and enters the lytic cycle to produce virus particles. At the onset of the lytic cycle, the virus expresses two immediate-early transcription factors, Rta and Zta, which activate EBV’s lytic genes. The genes encoding Rta and Zta, BRLF1 and BZLF1, respectively, are situated adjacent on the viral genome with BRLF1 located upstream. The promoter of BRLF1 (Rp) transcribes a bicistronic BRLF1-BZLF1 mRNA (RZ-mRNA). Earlier study has established that Zta is translated efficiently from the bicistronic mRNA; Rta can elevate the translation of BZLF1 orf located downstream in cis via the intercistronic region (ICR) on the RZ-mRNA in P3HR1 B lymphocytes. This study finds that Rta can trans-activate the BZLF1 translation in 293T cells. By generating a bicistronic reporter plasmid (pEGFP-ICR-Luc), this study verified that Rta acts as an IRES trans-acting factor (ITAF) to activate downstream translation in a trans-acting manner and the N-terminal domain of Rta is essential in the scheme. Deletion analysis of ICR further indicates that the two regions within ICR, region I and region II, are important for the translational activation by Rta. Moreover, RNA-protein pulldown assay confirms that Rta binds to ICR in vitro. Altogether, this study demonstrated that the ICR in RZ-mRNA function as an IRES, while Rta serve as an ITAF that trans-activates the translation of BZLF1 from BRLF1-BZLF1 bicistronic mRNA, thereby promoting the expression of Zta.
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