Barends Sharief, Rudinger-Thirion Joëlle, Florentz Catherine, Giegé Richard, Pleij Cornelis W A, Kraal Barend
UPR 9002 du CNRS, IBMC, F-67084 Strasbourg Cedex, France.
J Virol. 2004 Apr;78(8):4003-10. doi: 10.1128/jvi.78.8.4003-4010.2004.
For various groups of plant viruses, the genomic RNAs end with a tRNA-like structure (TLS) instead of the 3' poly(A) tail of common mRNAs. The actual function of these TLSs has long been enigmatic. Recently, however, it became clear that for turnip yellow mosaic virus, a tymovirus, the valylated TLS(TYMV) of the single genomic RNA functions as a bait for host ribosomes and directs them to the internal initiation site of translation (with N-terminal valine) of the second open reading frame for the polyprotein. This discovery prompted us to investigate whether the much larger TLSs of a different genus of viruses have a comparable function in translation. Brome mosaic virus (BMV), a bromovirus, has a tripartite RNA genome with a subgenomic RNA4 for coat protein expression. All four RNAs carry a highly conserved and bulky 3' TLS(BMV) (about 200 nucleotides) with determinants for tyrosylation. We discovered TLS(BMV)-catalyzed self-tyrosylation of the tyrosyl-tRNA synthetase but could not clearly detect tyrosine incorporation into any virus-encoded protein. We established that BMV proteins do not need TLS(BMV) tyrosylation for their initiation. However, disruption of the TLSs strongly reduced the translation of genomic RNA1, RNA2, and less strongly, RNA3, whereas coat protein expression from RNA4 remained unaffected. This aberrant translation could be partially restored by providing the TLS(BMV) in trans. Intriguingly, a subdomain of the TLS(BMV) could even almost fully restore translation to the original pattern. We discuss here a model with a central and dominant role for the TLS(BMV) during the BMV infection cycle.
对于各类植物病毒而言，其基因组RNA的末端是一个类似tRNA的结构（TLS），而非普通mRNA的3' 聚腺苷酸尾巴。这些TLS的实际功能长期以来一直是个谜。然而，最近有研究表明，对于芜菁黄花叶病毒（一种芜菁黄花叶病毒属病毒）来说，单基因组RNA的缬氨酰化TLS（TYMV）充当宿主核糖体的诱饵，并将它们引导至第二个开放阅读框（用于多聚蛋白，N端为缬氨酸）的内部翻译起始位点。这一发现促使我们去研究不同病毒属中更大的TLS在翻译过程中是否具有类似功能。雀麦花叶病毒（BMV）是一种雀麦花叶病毒属病毒，具有一个三分体RNA基因组以及一个用于外壳蛋白表达的亚基因组RNA4。所有这四种RNA都带有一个高度保守且庞大的3' TLS（BMV）（约200个核苷酸），其中含有酪氨酰化的决定因素。我们发现了TLS（BMV）催化的酪氨酰 - tRNA合成酶的自身酪氨酰化，但未能明确检测到酪氨酸掺入任何病毒编码蛋白中。我们确定BMV蛋白的起始并不需要TLS（BMV）的酪氨酰化。然而，TLS的破坏会强烈降低基因组RNA1、RNA2的翻译，对RNA3的影响较小，而RNA4的外壳蛋白表达则不受影响。通过反式提供TLS（BMV），这种异常翻译可以部分恢复。有趣的是，TLS（BMV）的一个亚结构域甚至几乎可以完全将翻译恢复到原始模式。我们在此讨论一个在BMV感染周期中TLS（BMV）起核心和主导作用的模型。
