Department of Chemistry and Biochemistry, University of Colorado, UCB 215, Boulder, Colorado 80309, United States.
Biochemistry. 2010 Nov 30;49(47):10208-15. doi: 10.1021/bi101011j. Epub 2010 Nov 8.
The influenza RNA-dependent RNA polymerase (RdRp) both replicates the flu's RNA genome and transcribes its mRNA. Replication occurs de novo; however, initiation of transcription requires a 7-methylguanosine 5'-capped primer that is "snatched" from host mRNA via endonuclease and cap binding functions of the influenza polymerase. A key question is how the virus regulates the relative amounts of transcription and replication. We found that the concentration of a capped cellular mRNA, the concentration of the 5' end of the viral RNA, and the concentration of RdRp all regulate the relative amounts of replication versus transcription. The host mRNA, from which the RdRp snatches its capped primer, acts to upregulate transcription and repress replication. Elevated concentrations of the RdRp itself switch the influenza polymerase toward replication, likely through an oligomerization of the polymerase. The 5' end of the vRNA template both activates replication and inhibits transcription of the vRNA template, thereby indicating that RdRp contains an allosteric binding site for the 5' end of the vRNA template. These data provide insights into the regulation of RdRp throughout the viral life cycle and how it synthesizes the appropriate amounts of viral mRNA and replication products (vRNA and cRNA).
流感 RNA 依赖性 RNA 聚合酶（RdRp）既能复制流感病毒的 RNA 基因组，也能转录其 mRNA。复制是从头开始的；然而，转录的起始需要一个 7-甲基鸟苷 5′-帽结构的引物，该引物通过流感聚合酶的内切核酸酶和帽结合功能从宿主 mRNA 中“抢夺”。一个关键问题是病毒如何调节转录和复制的相对数量。我们发现，被 RdRp 抢夺其帽结构引物的细胞 mRNA 的浓度、病毒 RNA 5' 端的浓度以及 RdRp 的浓度都调节着复制相对于转录的相对数量。宿主 mRNA 通过 RdRp 自身的寡聚化，从其中抢夺其帽结构引物，从而上调转录并抑制复制。RdRp 浓度的升高会使流感聚合酶偏向于复制，这可能是通过聚合酶的寡聚化实现的。vRNA 模板的 5' 端既能激活复制，又能抑制 vRNA 模板的转录，这表明 RdRp 包含一个 vRNA 模板 5' 端的变构结合位点。这些数据为 RdRp 在整个病毒生命周期中的调控以及它如何合成适当数量的病毒 mRNA 和复制产物（vRNA 和 cRNA）提供了深入的了解。
