An umbraviral protein, involved in long-distance RNA movement, binds viral RNA and forms unique, protective ribonucleoprotein complexes
An umbraviral protein, involved in long-distance RNA movement, binds viral RNA and forms unique, protective ribonucleoprotein complexes
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DOI：
10.1128/jvi.77.5.3031-3040.2003
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发表时间：
2003-03-01
影响因子：
5.4
通讯作者：
Oparka, KJ
中科院分区：
文献类型：
--
作者：
Taliansky, M;Roberts, IM;Oparka, KJ
UmbraVirus与大多数其他病毒的不同之处在于，它们不编码传统的衣壳蛋白(CP)；因此，在受感染的植物中不会形成可识别的病毒颗粒。它们缺乏CP被ORF3蛋白弥补，ORF3蛋白完成由其他病毒的CP提供的功能，如保护和病毒RNA的长距离移动。由烟草花叶病毒(TMV)表达的花生丛病毒(GRV)ORF3蛋白代替TMV CP[TMV(ORF3)]，在感染细胞中与TMV RNA相互作用形成丝状核糖核蛋白(RNP)颗粒，该颗粒具有螺旋结构，但不像经典病毒粒子那样均匀。这些RNP颗粒在细胞质中的无定形包裹体中观察到，它们嵌入在电子致密的基质材料中。内涵体存在于所有类型的细胞中，并且在韧皮部伴生细胞中含量丰富，尤其是伴生细胞和未成熟的筛子分子。从感染烟草花叶病毒(ORF3)或GRV本身的植物中分离到外观与包裹体相似的RNP复合体。在体外，ORF3蛋白形成寡聚体并结合RNA，其方式与其在形成RNP复合体中的作用一致。这表明ORF3蛋白形成的细胞质RNP复合体对病毒RNA具有保护作用，可能是病毒通过韧皮部的形式。因此，这里检测到的RNP颗粒代表了一种新的结构，可以被枝状病毒用作经典病毒粒子的替代品。
Umbraviruses are different from most other viruses in that they do not encode a conventional capsid protein (CP); therefore, no recognizable virus particles are formed in infected plants. Their lack of a CP is compensated for by the ORF3 protein, which fulfils functions that are provided by the CPs of other viruses, such as protection and long-distance movement of viral RNA. When the Groundnut rosette virus (GRV) ORF3 protein was expressed from Tobacco mosaic virus (TMV) in place of the TMV CP [TMV(ORF3)], in infected cells it interacted with the TMV RNA to form filamentous ribonucleoprotein (RNP) particles that had elements of helical structure but were not as uniform as classical virions. These RNP particles were observed in amorphous inclusions in the cytoplasm, where they were embedded within an electron-dense matrix material. The inclusions were detected in all types of cells and were abundant in phloem-associated cells, in particular companion cells and immature sieve elements. RNP-containing complexes similar in appearance to the inclusions were isolated from plants infected with TMV(ORF3) or with GRV itself. In vitro, the ORF3 protein formed oligomers and bound RNA in a manner consistent with its role in the formation of RNP complexes. It is suggested that the cytoplasmic RNP complexes formed by the ORF3 protein serve to protect viral RNA and may be the form in which it moves through the phloem. Thus, the RNP particles detected here represent a novel structure which may be used by umbraviruses as an alternative to classical virions.