2019-08-012024-05-18https://scholars.lib.ntu.edu.tw/handle/123456789/702591摘要：EB病毒 (EBV) 具有潛伏期及溶裂期兩個不同的生命史，而溶裂期是由 Rta 與 Zta 這兩個病毒轉錄因子所活化。這兩個蛋白質分別是由 EBV 基因組上的兩個相鄰基因 BRLF1 與 BZLF1 所表達。雖然兩個基因都各有自己的啟動子，但由 BRLF1 啟動子所轉錄的雙基因mRNA 同時帶有上游 BRLF1 與下游 BZLF1 開放譯讀架 (orf)，其中間是由 210 個核&#33527;酸的順反子間區 (ICR) 將其區隔。雖然雙基因 mRNA 下游的 orf 很少被轉譯甚至完全不轉譯，但是EBV 卻能有效地轉譯出這個雙基因mRNA 中 的BZLF1 orf 。在先前研究中已經發現雙基因 mRNA 中的 BZLF1 orf的轉譯需要 Rta 與 ICR 內的region I 中一個 40 bp 的序列。我們目前的研究發現 Rta 會和 18S rRNA 及 mRNA 的 5` 端帽結合。透過蔗糖梯度分析也發現 Rta 會和核醣體結合。更重要的是，Rta 在潛伏期也會表現並促進細胞內的整體轉譯。若在潛伏期抑制 Rta 的表現，則會降低細胞的存活率，顯示潛伏期表現的Rta 有利於細胞的增殖。在這項計畫中，我們假設 Rta 能夠將 40S 核醣體與轉譯起始因子聚集至 ICR 的 region I 位置，促進 BZLF1 orf 的轉譯起始。Rta 可能具有RNA螺旋&#37238;的活性或是作為 IRES trans-acting factor (ITAF)以 提升 BZLF1 orf 的轉譯起始。除此之外，這項研究將會證明 Rta 在潛伏期的 B 淋巴球內參與依賴 5` 端帽進行的轉譯起始作用，藉此提升細胞內的整體轉譯以及細胞存活。這項研究將會對 Rta 在潛伏期與溶裂期調控轉譯作用的機制提出新的見解，對於瞭解 EBV 的增殖及致癌性是非常關鍵的發現。<br> Abstract: Epstein-Barr virus (EBV) has distinct life cycles, latency and the lytic cycle. The lytic cycle is activated by two viral encoded transcription factors, Rta and Zta. These two proteins are encoded by two adjacently located genes on the EBV genome, BRLF1 and BZLF1, respectively. Although each of these two genes has its own promoter, the mRNA transcribed from the BRLF1 promoter is bicistronic, containing an upstream BRLF1 open reading frame (orf), and a downstream BZLF1 orf, with a 210-nucleotide (n.t.) intercistronic region (ICR) separating the two. Although the downstream orf in a bicistronic mRNA is usually translated poorly or not translated at all, BZLF1 orf is translated from the bicistronic mRNA efficiently by EBV. Earlier studies have shown that translating BZLF1 orf from the bicistronic mRNA requires Rta and a 40-n.t. region, called region I, in ICR. Our current study finds that Rta binds to 18S rRNA and the cap structure in mRNA. Sucrose fractionation analysis shows that Rta associates with ribosomes. Importantly, Rta is expressed at latency and promotes global translation. Knockdown of the level of Rta expression in latency reduces cell viability, suggesting that Rta benefits cell proliferation. In this proposal, we hypothesize that Rta recruits 40S ribosome and translational initiation factors to region I in ICR to facilitate translational initiation for the translation of the BZLF1 orf. Rta may have helicase activity or act as an IRES trans-acting factor (ITAF) to promote translational initiation of BZLF1 orf. Furthermore, this study will verify how latency’s Rta participates in 5’-cap dependent translation initiation in B lymphocytes, thereby leading to the increase of global translation and cell viability. This research will provide new insight into the mechanism by which Rta controls translation during latency and lytic cycle, which will be crucial to the understanding of EBV’s proliferation and oncogenesis.EB病毒Rta蛋白質intercistronic區域BRLF1-BZLF1雙基因mRNA轉譯起始Epstein-Barr virusRtaintercistronic regionbicistronic BRLF1-BZLF1 mRNAtranslation initiation