Neil Chris, Newman Joseph, Stonehouse Nicola J, Rowlands David J, Belsham Graham J, Tuthill Tobias J
The Pirbright Institute, Ash Road, Pirbright, Surrey, United Kingdom.
The Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom.
PLoS Pathog. 2024 Dec 23;20(12):e1012283. doi: 10.1371/journal.ppat.1012283. eCollection 2024 Dec.
Virus assembly is a crucial step for the completion of the viral replication cycle. In addition to ensuring efficient incorporation of viral genomes into nascent virions, high specificity is required to prevent incorporation of host nucleic acids. For picornaviruses, including FMDV, the mechanisms required to fulfil these requirements are not well understood. However, recent evidence has suggested that specific RNA sequences dispersed throughout picornavirus genomes are involved in packaging. Here, we have shown that such sequences are essential for FMDV RNA packaging and have demonstrated roles for both the pseudoknot (PK) region and the poly-(C) tract in this process, where the length of the poly-(C) tract was found to influence the efficiency of RNA encapsidation. Sub-genomic replicons containing longer poly-(C) tracts were packaged with greater efficiency in trans, and viruses recovered from transcripts containing short poly-(C) tracts were found to have greatly extended poly-(C) tracts after only a single passage in cells, suggesting that maintaining a long poly-(C) tract provides a selective advantage. We also demonstrated a critical role for a packaging signal (PS) located in the pseudoknot (PK) region, adjacent to the poly-(C) tract, as well as several other non-essential but beneficial PSs elsewhere in the genome. Collectively, these PSs greatly enhanced encapsidation efficiency, with the poly-(C) tract possibly facilitating nearby PSs to adopt the correct conformation. Using these data, we have proposed a model where interactions with capsid precursors control a transition between two RNA conformations, directing the fate of nascent genomes to either be packaged or alternatively to act as templates for replication and/or for protein translation.
病毒组装是病毒复制周期完成的关键步骤。除了确保病毒基因组高效整合到新生病毒粒子中，还需要高度特异性以防止宿主核酸的整合。对于包括口蹄疫病毒（FMDV）在内的小RNA病毒，满足这些要求所需的机制尚未完全了解。然而，最近的证据表明，分散在小RNA病毒基因组中的特定RNA序列参与了包装过程。在这里，我们已经表明这些序列对于FMDV RNA包装至关重要，并证明了假结（PK）区域和多聚（C）序列在此过程中的作用，其中发现多聚（C）序列的长度会影响RNA衣壳化的效率。含有更长多聚（C）序列的亚基因组复制子在反式包装中效率更高，并且从含有短多聚（C）序列的转录本中回收的病毒在细胞中仅传代一次后就发现其多聚（C）序列大大延长，这表明维持长的多聚（C）序列具有选择优势。我们还证明了位于假结（PK）区域、与多聚（C）序列相邻的包装信号（PS）以及基因组中其他几个非必需但有益的PS的关键作用。总的来说，这些PS大大提高了衣壳化效率，多聚（C）序列可能促进附近的PS采取正确的构象。利用这些数据，我们提出了一个模型，其中与衣壳前体的相互作用控制两种RNA构象之间的转变，引导新生基因组的命运要么被包装，要么作为复制和/或蛋白质翻译的模板。
