Department of Biological Sciences, Mississippi State University, Starkville, MS 39762, USA.
Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, OH 45237, USA.
Viruses. 2018 Sep 17;10(9):503. doi: 10.3390/v10090503.
Viroids are circular noncoding RNAs that infect plants. Without encoding any protein, these noncoding RNAs contain the necessary genetic information for propagation in hosts. Nuclear-replicating viroids employ DNA-dependent RNA polymerase II (Pol II) for replication, a process that makes a DNA-dependent enzyme recognize RNA templates. Recently, a splicing variant of transcription factor IIIA (TFIIIA-7ZF) was identified as essential for Pol II to replicate potato spindle tuber viroid (PSTVd). The expression of TFIIIA-7ZF, particularly the splicing event, is regulated by a ribosomal protein (RPL5). PSTVd modulates its expression through a direct interaction with RPL5 resulting in optimized expression of TFIIIA-7ZF. This review summarizes the recent discoveries of host factors and regulatory mechanisms underlying PSTVd-templated transcription processes and raises new questions that may help future exploration in this direction. In addition, it briefly compares the machinery and the regulatory mechanism for PSTVd with the replication/transcription system of human hepatitis delta virus.
类病毒是感染植物的环状非编码 RNA。这些非编码 RNA 不编码任何蛋白质，但包含在宿主中进行繁殖所需的遗传信息。核复制的类病毒利用依赖 DNA 的 RNA 聚合酶 II（Pol II）进行复制，这一过程使依赖 DNA 的酶识别 RNA 模板。最近，鉴定出转录因子 IIIA（TFIIIA-7ZF）的剪接变体对于 Pol II 复制马铃薯纺锤形块茎类病毒（PSTVd）是必不可少的。TFIIIA-7ZF 的表达，特别是剪接事件，受到核糖体蛋白（RPL5）的调控。PSTVd 通过与 RPL5 的直接相互作用来调节其表达，从而优化 TFIIIA-7ZF 的表达。这篇综述总结了 PSTVd 模板转录过程中宿主因子和调控机制的最新发现，并提出了可能有助于这一方向未来探索的新问题。此外，它还简要比较了 PSTVd 的复制/转录系统与人类乙型肝炎 delta 病毒的复制/转录系统的机制和调控机制。
