Wu B, White K A
Department of Biology, York University, Toronto, Ontario, Canada M3J 1P3.
J Virol. 1999 Nov;73(11):8982-8. doi: 10.1128/JVI.73.11.8982-8988.1999.
Tomato bushy stunt virus (TBSV) is a positive-strand RNA virus and is the prototype member of the genus Tombusvirus. The genomes of members of this genus are not polyadenylated, and prevailing evidence supports the absence of a 5' cap structure. Previously, a 167-nucleotide-long segment (region 3.5) located near the 3' terminus of the TBSV genome was implicated as a determinant of translational efficiency (S.K. Oster, B. Wu and K. A. White, J. Virol. 72:5845-5851, 1998). In the present report, we provide evidence that a 3'-proximal segment of the genome, which includes region 3.5, is involved in facilitating cap-independent translation. Our results indicate that (i) a 5' cap structure can substitute functionally for the absence of region 3.5 in viral and chimeric reporter mRNAs in vivo; (ii) deletion of region 3.5 from viral and chimeric mRNAs has no appreciable effect on message stability; (iii) region 3.5 represents part of a larger 3' proximal element, designated as the 3' cap-independent translational enhancer (3'CITE), that is required for proficient cap-independent translation; (iv) the 3'CITE also facilitates cap-dependent translation; (v) none of the major viral proteins are required for 3'CITE activity; and (vi) no significant 3'CITE-dependent stimulation of translation was observed when mRNAs were tested in vitro in wheat germ extract under various assay conditions. This latter property distinguishes the 3'CITE from other characterized plant viral 3'-proximal cap-independent translational enhancers. Additionally, because the 3'CITE overlaps with cis-acting replication signals, it could potentially participate in regulating the initiation of genome replication.
番茄丛矮病毒（TBSV）是一种正链RNA病毒，是番茄病毒属的原型成员。该属成员的基因组没有多聚腺苷酸化，现有证据支持其不存在5'帽结构。此前，位于TBSV基因组3'末端附近的一段167个核苷酸长的片段（区域3.5）被认为是翻译效率的决定因素（S.K.奥斯特、B.吴和K.A.怀特，《病毒学杂志》72:5845 - 5851，1998）。在本报告中，我们提供证据表明基因组的3'近端片段，包括区域3.5，参与促进不依赖帽的翻译。我们的结果表明：（i）在体内，5'帽结构在功能上可以替代病毒和嵌合报告mRNA中区域3.5的缺失；（ii）从病毒和嵌合mRNA中删除区域3.5对mRNA稳定性没有明显影响；（iii）区域3.5代表一个更大的3'近端元件的一部分，称为3'不依赖帽翻译增强子（3'CITE），它是高效不依赖帽翻译所必需的；（iv）3'CITE也促进依赖帽的翻译；（v）3'CITE活性不需要任何主要病毒蛋白；（vi）当在各种测定条件下于小麦胚芽提取物中对mRNA进行体外测试时，未观察到明显的3'CITE依赖性翻译刺激。后一特性将3'CITE与其他已表征的植物病毒3'近端不依赖帽翻译增强子区分开来。此外，由于3'CITE与顺式作用复制信号重叠，它可能潜在地参与调节基因组复制的起始。
