State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin 150069, China.
Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA.
Viruses. 2021 Oct 26;13(11):2159. doi: 10.3390/v13112159.
Senecavirus A (SVA) is a picornavirus that causes vesicular disease in swine and the only member of the genus. Like in all members of , the 5' untranslated region (5'UTR) of SVA contains an internal ribosome entry site (IRES) that initiates cap-independent translation. For example, the replacement of the IRES of foot-and-mouth disease virus (FMDV) with its relative bovine rhinitis B virus (BRBV) affects the viral translation efficiency and virulence. Structurally, the IRES from SVA resembles that of hepatitis C virus (HCV), a flavivirus. Given the roles of the IRES in cap-independent translation for picornaviruses, we sought to functionally characterize the IRES of this genus by studying chimeric viruses generated by exchanging the native SVA IRES with that of HCV either entirely or individual domains. First, the results showed that a chimeric SVA virus harboring the IRES from HCV, H-SVA, is viable and replicated normally in rodent-derived BHK-21 cells but displays replication defects in porcine-derived ST cells. In the generation of chimeric viruses in which domain-specific elements from SVA were replaced with those of HCV, we identified an essential role for the stem-loop I element for IRES activity and recombinant virus recovery. Furthermore, a series of stem-loop I mutants allowed us to functionally characterize discrete IRES regions and correlate impaired IRES activities, using reporter systems with our inability to recover recombinant viruses in two different cell types. Interestingly, mutant viruses harboring partially defective IRES were viable. However, no discernable replication differences were observed, relative to the wild-type virus, suggesting the cooperation of additional factors, such as intermolecular viral RNA interactions, act in concert in regulating IRES-dependent translation during infection. Altogether, we found that the stem-loop I of SVA is an essential element for IRES-dependent translation activity and viral replication.
塞尼卡病毒 A（SVA）是一种引起猪水疱病的微小核糖核酸病毒，是该属的唯一成员。与微小核糖核酸病毒属的所有成员一样，SVA 的 5'非翻译区（5'UTR）含有一个内部核糖体进入位点（IRES），该位点启动帽非依赖性翻译。例如，用相对的牛鼻气管炎 B 病毒（BRBV）替换口蹄疫病毒（FMDV）的 IRES 会影响病毒的翻译效率和毒力。从结构上看，SVA 的 IRES 类似于丙型肝炎病毒（HCV），一种黄病毒。鉴于 IRES 在微小核糖核酸病毒的帽非依赖性翻译中的作用，我们试图通过研究用 HCV 的 IRES 完全或单独结构域替换 SVA 的天然 IRES 产生的嵌合病毒来对该属的 IRES 进行功能表征。首先，结果表明，含有 HCV IRES 的嵌合 SVA 病毒 H-SVA 是可行的，并且可以在啮齿动物源性 BHK-21 细胞中正常复制，但在猪源性 ST 细胞中显示出复制缺陷。在用 HCV 的结构域特异性元件替换嵌合病毒中 SVA 的特定元件的过程中，我们确定了茎环 I 元件对 IRES 活性和重组病毒恢复的重要作用。此外，一系列茎环 I 突变体使我们能够使用报告系统在两种不同的细胞类型中无法回收重组病毒的情况下，对离散的 IRES 区域进行功能表征，并将其与受损的 IRES 活性相关联。有趣的是，携带部分缺陷 IRES 的突变病毒是可行的。然而，与野生型病毒相比，没有观察到明显的复制差异，这表明在感染过程中，需要其他因素（如分子间病毒 RNA 相互作用）的合作来协同调节 IRES 依赖性翻译。总之，我们发现 SVA 的茎环 I 是 IRES 依赖性翻译活性和病毒复制所必需的元件。
