Wierzchoslawski Rafal, Urbanowicz Anna, Dzianott Aleksandra, Figlerowicz Marek, Bujarski Jozef J
Plant Molecular Biology Center and the Department of Biological Sciences, Montgomery Hall, Northern Illinois University, De Kalb, IL 60115, USA.
J Virol. 2006 Dec;80(24):12357-66. doi: 10.1128/JVI.01207-06. Epub 2006 Sep 27.
The synthesis of 3' subgenomic RNA4 (sgRNA4) by initiation from an internal sg promoter in the RNA3 segment was first described for Brome mosaic bromovirus (BMV), a model tripartite positive-sense RNA virus (W. A. Miller, T. W. Dreher, and T. C. Hall, Nature 313:68-70, 1985). In this work, we describe a novel 5' sgRNA of BMV (sgRNA3a) that we propose arises by premature internal termination and that encapsidates in BMV virions. Cloning and sequencing revealed that, unlike any other BMV RNA segment, sgRNA3a carries a 3' oligo(A) tail, in which respect it resembles cellular mRNAs. Indeed, both the accumulation of sgRNA3a in polysomes and the synthesis of movement protein 3a in in vitro systems suggest active functions of sgRNA3a during protein synthesis. Moreover, when copied in the BMV replicase in vitro reaction, the minus-strand RNA3 template generated the sgRNA3a product, likely by premature termination at the minus-strand oligo(U) tract. Deletion of the oligo(A) tract in BMV RNA3 inhibited synthesis of sgRNA3a during infection. We propose a model in which the synthesis of RNA3 is terminated prematurely near the sg promoter. The discovery of 5' sgRNA3a sheds new light on strategies viruses can use to separate replication from the translation functions of their genomic RNAs.
3'亚基因组RNA4（sgRNA4）通过起始于RNA3片段中的内部sg启动子进行合成，这首先是在雀麦花叶病毒（BMV）中被描述的，BMV是一种典型的三分体正义RNA病毒（W. A. 米勒、T. W. 德雷尔和T. C. 霍尔，《自然》313:68 - 70，1985）。在这项研究中，我们描述了一种新型的BMV 5' sgRNA（sgRNA3a），我们认为它是由内部过早终止产生的，并能包装进BMV病毒粒子中。克隆和测序显示，与任何其他BMV RNA片段不同，sgRNA3a带有一个3'寡聚腺苷酸尾巴，在这方面它类似于细胞mRNA。实际上，sgRNA3a在多核糖体中的积累以及体外系统中运动蛋白3a的合成表明sgRNA3a在蛋白质合成过程中具有活跃功能。此外，当在体外BMV复制酶反应中进行复制时，负链RNA3模板产生了sgRNA3a产物，可能是通过在负链寡聚尿苷酸区域过早终止。在感染过程中删除BMV RNA3中的寡聚腺苷酸区域会抑制sgRNA3a的合成。我们提出了一个模型，其中RNA3的合成在sg启动子附近过早终止。5' sgRNA3a的发现为病毒可用于将复制与其基因组RNA的翻译功能分开的策略提供了新的见解。
