Chernysheva Olena A, White K Andrew
Department of Biology, York University, Toronto, 4700 Keele Street, Ontario, Canada M3J 1P3.
Virology. 2005 Feb 20;332(2):640-9. doi: 10.1016/j.virol.2004.12.003.
Satellite (sat) RNAs are parasitic sub-viral RNA replicons found associated with certain positive-strand RNA viruses. Typical sat RNAs, such as those associated with members of the genus Tombusvirus, share little or no sequence identity with their helper virus genomes. Here, we have investigated a tombusvirus sat RNA and determined that it contains two functionally-relevant higher-order RNA domains, a T-shaped domain and a downstream domain, that are similar to elements shown previously to be present in the 5' untranslated regions (UTRs) of tombusvirus genomes. Although the two sat RNA domains showed only limited sequence identity with their viral counterparts, they were able to adopt comparably-folded RNA secondary structures. Interestingly, the relative spacing between the domains in the viral and satellite contexts was notably different. In the viral 5' UTR, the two domains are adjacent and separated by a small hairpin, however, in the sat RNA they are separated by a 137-nt long segment. Despite this distal modular arrangement, the two domains were found to be united spatially in the sat RNA through the formation of an RNA-RNA bridge. This co-localization facilitated an important inter-domain interaction and was essential for efficient helper-mediated sat RNA accumulation in protoplasts. These results indicate that the tombusvirus sat RNA and helper genome contain structurally and functionally equivalent RNA domains. It is proposed that the limited sequence identity observed between these corresponding higher-order RNA structures is related to a strategy that reduces the induction of gene silencing, which presumably would be detrimental to both viral and sat RNA replicons.
卫星（sat）RNA是一类寄生性亚病毒RNA复制子，与某些正链RNA病毒相关。典型的sat RNA，如那些与番茄丛矮病毒属成员相关的sat RNA，与其辅助病毒基因组几乎没有或完全没有序列同源性。在这里，我们研究了一种番茄丛矮病毒sat RNA，并确定它包含两个功能相关的高阶RNA结构域，一个T形结构域和一个下游结构域，它们类似于先前在番茄丛矮病毒基因组的5'非翻译区（UTR）中发现的元件。尽管这两个sat RNA结构域与其病毒对应物仅显示出有限的序列同源性，但它们能够形成类似折叠的RNA二级结构。有趣的是，在病毒和卫星环境中，这些结构域之间的相对间距明显不同。在病毒的5'UTR中，这两个结构域相邻，由一个小发夹隔开，然而，在sat RNA中，它们由一个137个核苷酸长的片段隔开。尽管有这种远距离的模块化排列，但发现这两个结构域在sat RNA中通过形成RNA-RNA桥在空间上结合在一起。这种共定位促进了重要的结构域间相互作用，对于原生质体中辅助病毒介导的sat RNA高效积累至关重要。这些结果表明，番茄丛矮病毒sat RNA和辅助病毒基因组包含结构和功能上等效的RNA结构域。有人提出，在这些相应的高阶RNA结构之间观察到的有限序列同源性与一种减少基因沉默诱导的策略有关，基因沉默可能对病毒和sat RNA复制子都有害。
