Viral RNA-dependent RNA polymerases (RdRPs) play central roles in the genome replication and transcription processes of RNA viruses. RdRPs initiate RNA synthesis either in primer-dependent or de novo mechanism, with the latter often assisted by a ‘priming element’ (PE) within the RdRP thumb domain. However, RdRP PEs exhibit high-level structural diversity, making it difficult to reconcile their conserved function in de novo initiation. Here we determined a 3.1-Å crystal structure of the Flaviviridae classical swine fever virus (CSFV) RdRP with a relative complete PE. Structure-based mutagenesis in combination with enzymology data further highlights the importance of a glycine residue (G671) and the participation of residues 665–680 in RdRP initiation. When compared with other representative Flaviviridae RdRPs, CSFV RdRP PE is structurally distinct but consistent in terminal initiation preference. Taken together, our work suggests that a conformational change in CSFV RdRP PE is necessary to fulfill de novo initiation, and similar ‘induced-fit’ mechanisms may be commonly taken by PE-containing de novo viral RdRPs.

中文翻译：

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一种由瘟病毒 RNA 依赖性 RNA 聚合酶提出的诱导适应从头启动机制

病毒 RNA 依赖性 RNA 聚合酶 (RdRP) 在 RNA 病毒的基因组复制和转录过程中起着核心作用。RdRP 以引物依赖或从头机制启动 RNA 合成，后者通常由 RdRP 拇指域内的“启动元件”(PE) 辅助。然而，RdRP PE 表现出高水平的结构多样性，因此很难在从头启动中协调它们的保守功能。在这里，我们确定了具有相对完整 PE 的黄病毒科经典猪瘟病毒 (CSFV) RdRP 的 3.1-Å 晶体结构。基于结构的诱变结合酶学数据进一步强调了甘氨酸残基 (G671) 和残基 665-680 参与 RdRP 起始的重要性。与其他具有代表性的黄病毒科 RdRP 相比，CSFV RdRP PE 在结构上是不同的，但在终端启动偏好方面是一致的。总之，我们的工作表明，CSFV RdRP PE 的构象变化对于实现从头启动是必要的，并且含有 PE 的从头病毒 RdRP 通常可能采用类似的“诱导适应”机制。