Institut für Immunologie, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany.
Institut für Immunologie, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany
J Virol. 2020 Jul 16;94(15). doi: 10.1128/JVI.00280-20.
Caliciviruses have a positive-strand RNA genome with a length of about 7.5 kb that contains 2, 3, or 4 functional open reading frames (ORFs). A subgenomic mRNA (sg-RNA) is transcribed in the infected cell, and both major capsid protein viral protein 1 (VP1) and minor capsid protein VP2 are translated from the sg-RNA. Translation of proteins from the genomic RNA (g-RNA) and from the sg-RNA is mediated by the RNA-linked viral protein VPg (virus protein, genome linked). Most of the calicivirus genera have translation mechanisms leading to VP1 expression from the g-RNA. VP1 is part of the polyprotein for sapoviruses, lagoviruses, and neboviruses, and a termination/reinitiation mechanism was described for noroviruses. Vesiviruses have no known mechanism for the expression of VP1 from the g-RNA, and the genus is the only genus of the that generates VP1 via a precursor capsid leader protein (LC-VP1). Analyses of feline calicivirus (FCV) g-RNA translation showed a low level of VP1 expression with an initiation downstream of the original start codon of LC-VP1, leading to a smaller, truncated LC-VP1 (tLC-VP1) protein. Deletion and substitution analyses of the region surrounding the LC-VP1 start codon allowed the identification of sequences within the leader protein coding region of FCV that have an impact on VP1 translation frequency from the g-RNA. Introduction of such mutations into the virus showed an impact of strongly reduced tLC-VP1 levels translated from the g-RNA on viral replication. Caliciviruses are a cause of important diseases in humans and animals. It is crucial to understand the prerequisites of efficient replication of these viruses in order to develop strategies for prevention and treatment of these diseases. It was shown before that all caliciviruses except vesiviruses have established mechanisms to achieve major capsid protein (VP1) translation from the genomic RNA. Here, we show for the first time that a member of the genus also has a translation initiation mechanism by which a precursor protein of the VP1 protein is expressed from the genomic RNA. This finding clearly points at a functional role of the calicivirus VP1 capsid protein in early replication, and we provide experimental data supporting this hypothesis.
杯状病毒具有长度约为 7.5kb 的正链 RNA 基因组，包含 2、3 或 4 个功能开放阅读框 (ORF)。在感染细胞中转录亚基因组 mRNA (sg-RNA)，主要衣壳蛋白病毒蛋白 1 (VP1) 和次要衣壳蛋白 VP2 均从 sg-RNA 翻译。基因组 RNA (g-RNA) 和 sg-RNA 上翻译的蛋白质由 RNA 连接的病毒蛋白 VPg（病毒蛋白，基因组连接）介导。大多数杯状病毒属具有导致 g-RNA 上 VP1 表达的翻译机制。VP1 是 sapoviruses、lagoviruses 和 neboviruses 的多蛋白的一部分，并且 noroviruses 描述了终止/重新启动机制。Vesiviruses 没有已知的机制可从 g-RNA 表达 VP1，并且该属是唯一通过前衣壳先导蛋白 (LC-VP1) 产生 VP1 的属。对猫杯状病毒 (FCV) g-RNA 翻译的分析显示，VP1 的表达水平较低，起始于 LC-VP1 的原始起始密码子下游，导致较小的截短 LC-VP1 (tLC-VP1) 蛋白。LC-VP1 起始密码子周围区域的缺失和替换分析允许鉴定 FCV 先导蛋白编码区中对 g-RNA 上 VP1 翻译频率有影响的序列。将这些突变引入病毒中表明，从 g-RNA 翻译的 tLC-VP1 水平大大降低对病毒复制的影响。杯状病毒是人类和动物重要疾病的病因。了解这些病毒有效复制的前提条件对于开发这些疾病的预防和治疗策略至关重要。以前已经表明，除了 vesiviruses 之外，所有杯状病毒都建立了从基因组 RNA 实现主要衣壳蛋白 (VP1) 翻译的机制。在这里，我们首次表明，属的一个成员也具有翻译起始机制，通过该机制从基因组 RNA 表达 VP1 蛋白的前体蛋白。这一发现清楚地表明杯状病毒 VP1 衣壳蛋白在早期复制中具有功能作用，并且我们提供了支持该假说的实验数据。
