Paul A V, van Boom J H, Filippov D, Wimmer E
Department of Molecular Genetics and Microbiology, School of Medicine, Health Science Center, State University of New York, Stony Brook 11794-5222, USA.
Nature. 1998 May 21;393(6682):280-4. doi: 10.1038/30529.
A small protein, VPg, is covalently linked to the 5' end of the plus-stranded poliovirus genomic RNA. Poliovirus messenger RNA, identical in nucleotide sequence to genomic RNA, is not capped at its 5' end by the methylated structure that is common to most eukaryotic mRNAs. These discoveries presented two problems. First, as cap structures are usually required for translation of mRNA into protein, how does this uncapped viral RNA act as a template for translation? Second, what is the function of VPg? The identification of the internal ribosomal-entry site, which allows the entry of ribosomes into viral mRNA independently of the 5' mRNA end, has solved the first conundrum. Here we describe the resolution of the second problem. VPg is linked to the genomic RNA through the 5'-terminal uridylic acid of the RNA. We show that VPg can be uridylylated by the poliovirus RNA polymerase 3Dpol. Uridylylated VPg can then prime the transcription of polyadenylate RNA by 3Dpol to produce VPg-linked poly(U). Initiation of transcription of the poliovirus genome from the polyadenylated 3' end therefore depends on VPg.
一种小蛋白VPg共价连接于正链脊髓灰质炎病毒基因组RNA的5'端。脊髓灰质炎病毒信使RNA在核苷酸序列上与基因组RNA相同，其5'端没有大多数真核生物mRNA常见的甲基化结构加帽。这些发现带来了两个问题。第一，由于帽结构通常是mRNA翻译成蛋白质所必需的，这种未加帽的病毒RNA如何作为翻译模板？第二，VPg的功能是什么？内部核糖体进入位点的鉴定，使核糖体能够独立于mRNA的5'端进入病毒mRNA，解决了第一个难题。在此我们描述第二个问题的解决方案。VPg通过RNA的5'-末端尿苷酸与基因组RNA相连。我们发现VPg可被脊髓灰质炎病毒RNA聚合酶3Dpol尿苷酸化。尿苷酸化的VPg随后可由3Dpol引发聚腺苷酸RNA的转录，以产生与VPg相连的聚（U）。因此，从聚腺苷酸化的3'端起始脊髓灰质炎病毒基因组的转录依赖于VPg。
