Shwed Philip S, Dobos Peter, Cameron Lynne A, Vakharia Vikram N, Duncan Roy
Department of Microbiology, University of Guelph, Guelph, Ontario, Canada.
Virology. 2002 May 10;296(2):241-50. doi: 10.1006/viro.2001.1334.
We have cloned and characterized the Drosophila X virus (DXV) genome segment B and its encoded VP1, the putative RNA-dependent RNA polymerase (RdRp) present in the virion. The 2991-bp open reading frame encodes the largest birnavirus VP1 at 977 aa, with a calculated M(r) of 112.8 kDa. As with the VP1 proteins of the type species of the other two genera in the family Birnaviridae, namely, infectious pancreatic necrosis virus (genus Aquabirnavirus) and infectious bursal disease virus (genus Avibirnavirus), the DXV (genus Entomobirnavirus) VP1 protein contains a consensus GTP-binding site and appears to possess self-guanylylation activity. All of the birnavirus VP1 proteins contain conserved RdRp motifs that reside in the catalytic "palm" domain of all classes of polymerases. However, the birnavirus RdRps lack the highly conserved Gly-Asp-Asp (GDD) sequence, a component of the proposed catalytic site of this enzyme family that exists in the conserved motif VI of the palm domain of other RdRps. All three birnavirus RdRps do contain downstream DD motifs that could function as part of the catalytic triad. These motifs are, however, located in spatially distinct regions of the various birnavirus VP1 proteins. These results suggest that the VP1 proteins of birnaviruses form a defined subgroup of polymerases that either are lacking the conserved RdRp motif VI or have repositioned this motif to different structural regions.
我们已经克隆并鉴定了果蝇X病毒（DXV）的基因组片段B及其编码的VP1，VP1是病毒粒子中假定的RNA依赖性RNA聚合酶（RdRp）。2991个碱基对的开放阅读框编码了一个977个氨基酸的最大双RNA病毒VP1，计算分子量为112.8 kDa。与双RNA病毒科其他两个属的模式种的VP1蛋白一样，即传染性胰腺坏死病毒（水生双RNA病毒属）和传染性法氏囊病病毒（禽双RNA病毒属），DXV（昆虫双RNA病毒属）的VP1蛋白含有一个共有GTP结合位点，并且似乎具有自我鸟苷酸化活性。所有双RNA病毒的VP1蛋白都含有保守的RdRp基序，这些基序位于所有类型聚合酶的催化“手掌”结构域中。然而，双RNA病毒的RdRps缺乏高度保守的甘氨酸-天冬氨酸-天冬氨酸（GDD）序列，该序列是该酶家族假定催化位点的一个组成部分，存在于其他RdRps手掌结构域的保守基序VI中。所有三种双RNA病毒的RdRps确实都含有下游的DD基序，这些基序可以作为催化三联体的一部分发挥作用。然而，这些基序位于各种双RNA病毒VP1蛋白的空间不同区域。这些结果表明，双RNA病毒的VP1蛋白形成了一个确定的聚合酶亚组，该亚组要么缺乏保守的RdRp基序VI，要么已将该基序重新定位到不同的结构区域。
