Xu Wei, White K Andrew
Department of Biology, York University, Toronto, Ontario M3J 1P3, Canada.
J Virol. 2009 Oct;83(19):10096-105. doi: 10.1128/JVI.00376-09. Epub 2009 Jul 15.
Cucumber leaf spot virus (CLSV) is an aureusvirus (family Tombusviridae) that has a positive-sense RNA genome encoding five proteins. During infections, CLSV transcribes two subgenomic (sg) mRNAs and the larger of the two, sg mRNA1, encodes coat protein. Here, the viral RNA sequences and structures that regulate transcription and translation of CLSV sg mRNA1 were investigated. A medium-range RNA-RNA interaction in the CLSV genome, spanning 148 nucleotides, was found to be required for the efficient transcription of sg mRNA1. Further analysis indicated that the structure formed by this interaction acted as an attenuation signal required for transcription of sg mRNA1 via a premature termination mechanism. Translation of coat protein from sg mRNA1 was determined to be facilitated by a 5'-terminal stem-loop structure in the message that resembled a tRNA anticodon stem-loop. The results from mutational analysis indicated that the 5'-terminal stem-loop mediated efficient base pairing with a 3'-cap-independent translational enhancer at the 3' end of the message, leading to efficient translation of coat protein from sg mRNA1. Comparison of the regulatory RNA structures for sg mRNA1 of CLSV to those used by the closely related tombusviruses and certain cellular RNAs revealed interesting differences and similarities that provide evolutionary and mechanistic insights into RNA-based regulatory strategies.
黄瓜叶斑病毒（CLSV）是一种金病毒（番茄病毒科），其正义RNA基因组编码五种蛋白质。在感染过程中，CLSV转录两个亚基因组（sg）mRNA，其中较大的sg mRNA1编码外壳蛋白。在此，研究了调节CLSV sg mRNA1转录和翻译的病毒RNA序列和结构。发现CLSV基因组中一段跨越148个核苷酸的中程RNA-RNA相互作用是sg mRNA1有效转录所必需的。进一步分析表明，这种相互作用形成的结构通过提前终止机制作为sg mRNA1转录所需的衰减信号。确定sg mRNA1的外壳蛋白翻译是由该信使中类似于tRNA反密码子茎环的5'-末端茎环结构促进的。突变分析结果表明，5'-末端茎环介导与信使3'端的3'-帽依赖性翻译增强子进行有效碱基配对，从而导致sg mRNA1的外壳蛋白有效翻译。将CLSV的sg mRNA1的调控RNA结构与密切相关的番茄病毒和某些细胞RNA所使用的结构进行比较，发现了有趣的差异和相似之处，为基于RNA的调控策略提供了进化和机制方面的见解。
