VP1 and VP3 are required and sufficient for translation initiation of uncapped Infectious Bursal Disease Virus genomic dsRNA
VP1 and VP3 are required and sufficient for translation initiation of uncapped Infectious Bursal Disease Virus genomic dsRNA
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VP1 和 VP3 对于无帽传染性法氏囊病病毒基因组 dsRNA 的翻译起始是必需的且足够
DOI：
10.1128/jvi.01345-17
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发表时间：
2017
影响因子：
5.4
通讯作者：
Liu Hebin
中科院分区：
文献类型：
--
作者：
Ye Chengjin;Wang Yu;Zhang Enli;Han Xinpeng;Yu Zhaoli;Liu Hebin
传染性法氏囊病病毒（IBDV）是双RNA病毒科的双节段双链RNA（dsRNA）病毒。虽然IBDV基因组dsRNA缺乏5′帽，但未加帽的IBDV基因组RNA有效翻译的方法尚不清楚。在这项研究中，我们描述了一个帽独立的途径，翻译起始的IBDV无帽RNA依赖于VP 1和VP 3。我们表明，无论是纯化的IBDV基因组dsRNA，也没有脱帽病毒正义RNA转录直接翻译和拯救到宿主细胞中的感染性病毒。通过反式补充病毒蛋白VP 1和VP 3来挽救未加帽的IBDV基因组dsRNA的翻译缺陷，这取决于VP 1的完整聚合酶活性和VP 3的dsRNA结合活性。缺失分析表明，IBDV dsRNA的5′和3′非翻译区（UTR）是VP 1/VP 3依赖性翻译起始的必需区。值得注意的是，VP 1和VP 3还可以介导传染性IBDV从IBDV dsRNA的真实负义链的回收。此外，帽结合蛋白eIF 4 E的下调或抑制并没有减少，而是增强了VP 1/VP 3介导的未加帽IBDV RNA的翻译。总的来说，我们的发现首次揭示了VP 1和VP 3弥补了5′端帽的缺陷，并取代了eIF 4 E，赋予了未加帽的IBDV RNA翻译和拯救成感染性病毒的能力。目前的研究表明，未加帽的IBDV RNA不能通过宿主翻译机器直接翻译成病毒蛋白，因此是无感染性的。我们的研究结果构成了第一个直接的实验证据，即VP 1和VP 3是必需的，足以启动翻译的无帽IBDV基因组RNA作为一个替代帽和取代帽结合蛋白eIF 4 E。值得注意的是，VP 1/VP 3不仅介导传染性IBDV从IBDV dsRNA的正义链回收，而且还介导从IBDV dsRNA的负义链回收。这些发现不仅为IBDV生命周期的分子机制提供了新的见解，而且还为从病毒基因组dsRNA的正和负义链中回收IBDV的替代策略提供了新的工具。
Infectious bursal disease virus (IBDV) is a bisegmented double-strand RNA (dsRNA) virus of the Birnaviridae family. While IBDV genomic dsRNA lacks a 5′ cap, the means by which the uncapped IBDV genomic RNA is translated effectively is unknown. In this study, we describe a cap-independent pathway of translation initiation of IBDV uncapped RNA that relies on VP1 and VP3. We show that neither purified IBDV genomic dsRNA nor the uncapped viral plus-sense RNA transcripts were directly translated and rescued into infectious viruses in host cells. This defect in translation of the uncapped IBDV genomic dsRNA was rescued bytrans-supplementation of the viral proteins VP1 and VP3 which was dependent on both the intact polymerase activity of VP1 and the dsRNA binding activity of VP3. Deletion analysis showed that both 5′ and 3′ untranslated regions (UTRs) of IBDV dsRNA were essential for VP1/VP3-dependent translation initiation. Significantly, VP1 and VP3 could also mediate the recovery of infectious IBDV from the authentic minus-sense strand of IBDV dsRNA. Moreover, downregulation or inhibition of the cap-binding protein eIF4E did not decrease but, rather, enhanced the VP1/VP3-mediated translation of the uncapped IBDV RNA. Collectively, our findings for the first time reveal that VP1 and VP3 compensate for the deficiency of the 5′ cap and replace eIF4E to confer upon the uncapped IBDV RNA the ability to be translated and rescued into infectious viruses.IMPORTANCEA key point of control for virus replication is viral translation initiation. The current study shows that the uncapped IBDV RNA cannot be translated into viral proteins directly by host translation machinery and is thus noninfectious. Our results constitute the first direct experimental evidence that VP1 and VP3 are required and sufficient to initiate translation of uncapped IBDV genomic RNA by acting as a substitute for cap and replacing the cap-binding protein eIF4E. Significantly, VP1/VP3 mediate the recovery of infectious IBDV not only from the plus-sense strand but also from the minus-sense strand of the IBDV dsRNA. These findings provide not only new insights into the molecular mechanisms of the life cycle of IBDV but also a new tool for an alternative strategy for the recovery of IBDV from both the plus- and the minus-sense strands of the viral genomic dsRNA.