Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland 20742; email:
Annu Rev Microbiol. 2013;67:21-42. doi: 10.1146/annurev-micro-092412-155609. Epub 2013 May 13.
In the absence of a 5' cap, plant positive-strand RNA viruses have evolved a number of different elements in their 3' untranslated region (UTR) to attract initiation factors and/or ribosomes to their templates. These 3' cap-independent translational enhancers (3' CITEs) take different forms, such as I-shaped, Y-shaped, T-shaped, or pseudoknotted structures, or radiate multiple helices from a central hub. Common features of most 3' CITEs include the ability to bind a component of the translation initiation factor eIF4F complex and to engage in an RNA-RNA kissing-loop interaction with a hairpin loop located at the 5' end of the RNA. The two T-shaped structures can bind to ribosomes and ribosomal subunits, with one structure also able to engage in a simultaneous long-distance RNA-RNA interaction. Several of these 3' CITEs are interchangeable and there is evidence that natural recombination allows exchange of modular CITE units, which may overcome genetic resistance or extend the virus's host range.
在没有 5' 帽结构的情况下,植物正链 RNA 病毒在其 3' 非翻译区(UTR)中进化出了许多不同的元件,以吸引起始因子和/或核糖体与其模板结合。这些 3' 帽非依赖性翻译增强子(3' CITEs)有不同的形式,如 I 型、Y 型、T 型或假结结构,或从中心枢纽辐射出多个螺旋。大多数 3' CITE 的共同特征包括能够结合翻译起始因子 eIF4F 复合物的一个组成部分,并与位于 RNA 5' 端的发夹环进行 RNA-RNA 亲吻环相互作用。这两种 T 型结构都可以与核糖体和核糖体亚基结合,其中一种结构还能够同时进行长距离的 RNA-RNA 相互作用。其中一些 3' CITE 是可互换的,有证据表明自然重组允许模块化 CITE 单元的交换,这可能克服遗传抗性或扩大病毒的宿主范围。