Department of Microbiology and Viikki Plant Science Centre, University of Helsinki, 00014 Helsinki, Finland.
Viruses. 2020 Feb 11;12(2):197. doi: 10.3390/v12020197.
The interaction between the viral protein genome-linked (VPg) and eukaryotic initiation factor 4E (eIF4E) or eIF(iso)4E of the host plays a crucial role in potyvirus infection. The VPg of potato virus A (PVA) contains the Tyr-X-X-X-X-Leu-phi (YXXXLΦ) binding motif for eIF(iso)4E. In order to investigate its role in PVA infection, we substituted the conserved tyrosine and leucine residues of the motif with alanine residues in the infectious cDNA of PVA (PVA). PVA RNA replicated in infiltrated leaves, but RNA accumulation remained low. Systemic infection occurred only if a reversion to wild type PVA occurred. VPg was able to stabilize PVA RNA and enhance the expression of luciferase (3'RLUC) from the 3' end of the PVA genome. VPg could not support either PVA RNA stabilization or enhanced 3'RLUC expression. The RNA silencing suppressor helper-component proteinase (HCPro) is responsible for the formation of PVA-induced RNA granules (PGs) during infection. While VPg increased the number of PG-like foci, the percentage of PVA RNA co-localization with PGs was reduced from 86% to 20%. A testable hypothesis for future studies based on these results is that the binding of eIF(iso)4E to PVA VPg via the YXXXLΦ motif is required for PVA RNA stabilization, as well as the transfer to the RNA silencing suppression pathway and, further, to polysomes for viral protein synthesis.
病毒蛋白基因组连接（VPg）与宿主真核起始因子 4E（eIF4E）或 eIF（iso）4E 的相互作用在马铃薯 Y 病毒（PVA）感染中起着至关重要的作用。PVA 的 VPg 含有与 eIF（iso）4E 结合的 Tyr-X-X-X-X-Leu-phi（YXXXLΦ）基序。为了研究其在 PVA 感染中的作用，我们用丙氨酸取代了 PVA 传染性 cDNA 中基序的保守酪氨酸和亮氨酸残基（PVA）。PVA RNA 在浸润的叶片中复制，但 RNA 积累仍然很低。只有当 PVA 发生回复突变时，才会发生系统感染。VPg 能够稳定 PVA RNA，并增强 PVA 基因组 3'端的荧光素酶（3'RLUC）的表达。VPg 既不能支持 PVA RNA 的稳定，也不能增强 3'RLUC 的表达。RNA 沉默抑制辅助蛋白酶（HCPro）负责在感染过程中形成 PVA 诱导的 RNA 颗粒（PGs）。虽然 VPg 增加了 PG 样焦点的数量，但 PVA RNA 与 PG 共定位的百分比从 86%降低到 20%。根据这些结果，未来研究的一个可行假设是，通过 YXXXLΦ 基序，eIF（iso）4E 与 PVA VPg 的结合是 PVA RNA 稳定所必需的，以及转移到 RNA 沉默抑制途径，进一步转移到多核糖体进行病毒蛋白合成。
