Department of Molecular Biology, Umeå University, S-901 87 Umeå, Sweden.
Virus Res. 2011 Sep;160(1-2):51-8. doi: 10.1016/j.virusres.2011.05.006. Epub 2011 May 13.
The recently discovered Nora virus from Drosophila melanogaster is a single-stranded RNA virus. Its published genomic sequence encodes a typical picorna-like cassette of replicative enzymes, but no capsid proteins similar to those in other picorna-like viruses. We have now done additional sequencing at the termini of the viral genome, extending it by 455 nucleotides at the 5' end, but no more coding sequence was found. The completeness of the final 12,333-nucleotide sequence was verified by the production of infectious virus from the cloned genome. To identify the capsid proteins, we purified Nora virus particles and analyzed their proteins by mass spectrometry. Our results show that the capsid is built from three major proteins, VP4A, B and C, encoded in the fourth open reading frame of the viral genome. The viral particles also contain traces of a protein from the third open reading frame, VP3. VP4A and B are not closely related to other picorna-like virus capsid proteins in sequence, but may form similar jelly roll folds. VP4C differs from the others and is predicted to have an essentially α-helical conformation. In a related virus, identified from EST database sequences from Nasonia parasitoid wasps, VP4C is encoded in a separate open reading frame, separated from VP4A and B by a frame-shift. This opens a possibility that VP4C is produced in non-equimolar quantities. Altogether, our results suggest that the Nora virus capsid has a different protein organization compared to the order Picornavirales.
最近从黑腹果蝇中发现的 Nora 病毒是一种单链 RNA 病毒。它已公布的基因组序列编码了一种典型的微小 RNA 病毒样复制酶盒，但没有与其他微小 RNA 病毒样病毒相似的衣壳蛋白。我们现在已经在病毒基因组的末端进行了额外的测序，在 5' 端延长了 455 个核苷酸，但没有发现更多的编码序列。通过从克隆基因组中产生感染性病毒，验证了最终 12333 个核苷酸序列的完整性。为了鉴定衣壳蛋白，我们纯化了 Nora 病毒颗粒，并通过质谱分析了它们的蛋白质。我们的结果表明，衣壳由三个主要蛋白组成，即 VP4A、B 和 C，它们编码在病毒基因组的第四个开放阅读框中。病毒颗粒还含有第三个开放阅读框 VP3 蛋白的痕迹。VP4A 和 B 在序列上与其他微小 RNA 病毒的衣壳蛋白没有密切的关系，但可能形成类似的凝胶卷折叠。VP4C 与其他蛋白不同，预计具有基本的α-螺旋构象。在一种相关的病毒中，从寄生蜂 Nasonia 的 EST 数据库序列中鉴定出来，VP4C 编码在一个单独的开放阅读框中，通过移码与 VP4A 和 B 分开。这为 VP4C 以非等摩尔量产生提供了可能性。总的来说，我们的结果表明，与 Picornavirales 目相比，Nora 病毒的衣壳具有不同的蛋白质组织。
