Plant Pathology Department, University of Kentucky, Lexington, KY 40546-0312, USA.
J Virol. 2011 Jul;85(14):7343-52. doi: 10.1128/JVI.00364-11. Epub 2011 May 4.
The genome-length, dicistronic mRNA of the double-stranded RNA fungal virus Helminthosporium victoriae virus 190S (genus Victorivirus, family Totiviridae) contains two long open reading frames (ORFs) that overlap in the tetranucleotide AUGA. Translation of the downstream ORF, which encodes the RNA-dependent RNA polymerase (RdRp), has been proposed to depend on ribosomal reinitiation following termination of the upstream ORF, which encodes the capsid protein. In the current study, we examined the RNA sequence determinants for RdRp translation in this virus and demonstrated that a coupled termination-reinitiation (stop-restart) strategy is indeed used. Signals for termination-reinitiation are found within a 32-nucleotide stretch of RNA immediately upstream of the AUGA motif, including a predicted pseudoknot structure. The close proximity in which this predicted structure is followed by the upstream ORF's stop codon appears to be especially important for promoting translation of the downstream ORF. The normal strong preferences for an AUG start codon and the canonical sequence context to favor translation initiation appear somewhat relaxed for the downstream ORF. Similar sequence motifs and predicted RNA structures in other victoriviruses suggest that they all share a related stop-restart strategy for RdRp translation. Members of the genus Victorivirus thus provide new and unique opportunities for exploring the molecular mechanisms of translational coupling, which remain only partly understood in this and other systems.
双链 RNA 真菌病毒 Helminthosporium victoriae virus 190S(属 Victorivirus,家族 Totiviridae)的基因组长度、双顺反子 mRNA 包含两个长的开放阅读框 (ORF),在四核苷酸 AUGA 处重叠。据推测,下游 ORF(编码 RNA 依赖性 RNA 聚合酶 (RdRp))的翻译依赖于在上游 ORF(编码衣壳蛋白)终止后核糖体的重新起始。在当前的研究中,我们研究了该病毒中 RdRp 翻译的 RNA 序列决定因素,并证明确实使用了偶联终止-重新起始 (stop-restart) 策略。终止-重新起始的信号位于 AUGA 基序上游的 32 个核苷酸的 RNA 内,包括一个预测的假结结构。该预测结构紧随上游 ORF 的终止密码子,这似乎对促进下游 ORF 的翻译特别重要。下游 ORF 对 AUG 起始密码子的正常强烈偏好和有利于翻译起始的典型序列上下文似乎有些放宽。其他 victoriviruses 中的类似序列基元和预测的 RNA 结构表明,它们都共享 RdRp 翻译的相关停止-重新启动策略。因此,Victorivirus 属成员为探索翻译偶联的分子机制提供了新的和独特的机会,而在其他系统中,这种机制仍不完全了解。