Raijmakers Reinout, Egberts Wilma Vree, van Venrooij Walther J, Pruijn Ger J M
Department of Biochemistry, University of Nijmegen, Nijmegen, The Netherlands.
J Mol Biol. 2002 Nov 1;323(4):653-63. doi: 10.1016/s0022-2836(02)00947-6.
The exosome is a complex of 3'-->5' exoribonucleases, which functions in a variety of cellular processes, all requiring the processing or degradation of RNA. Here we present a model for the assembly of the six human RNase PH-like exosome subunits into a hexameric ring structure. In part, this structure is on the basis of the evolutionarily related bacterial degradosome, the core of which consists of three copies of the PNPase protein, each containing two RNase PH domains. In our model three additional exosome subunits, which contain S1 RNA-binding domains, are positioned on the outer surface of this ring. Evidence for this model was obtained by the identification of protein-protein interactions between individual exosome subunits in a mammalian two-hybrid system. In addition, the results of co-immunoprecipitation assays indicate that at least two copies of hRrp4p and hRrp41p are associated with a single exosome, suggesting that at least two of these ring structures are present in this complex. Finally, the identification of a human gene encoding the putative human counterpart of the bacterial PNPase protein is described, which suggests that the exosome is not the eukaryotic equivalent of the bacterial degradosome, although they do share similar functional activities.
外泌体是一种3'→5'外切核糖核酸酶复合物，在多种细胞过程中发挥作用，所有这些过程都需要对RNA进行加工或降解。在此，我们提出了一个关于六种人类核糖核酸酶PH样外泌体亚基组装成六聚体环结构的模型。部分而言，这种结构是基于进化上相关的细菌降解体，其核心由三个PNPase蛋白拷贝组成，每个拷贝包含两个核糖核酸酶PH结构域。在我们的模型中，另外三个包含S1 RNA结合结构域的外泌体亚基位于该环的外表面。通过在哺乳动物双杂交系统中鉴定单个外泌体亚基之间的蛋白质-蛋白质相互作用，获得了该模型的证据。此外，免疫共沉淀分析结果表明，至少两个拷贝的hRrp4p和hRrp41p与单个外泌体相关联，这表明该复合物中至少存在两个这样的环结构。最后，描述了一个编码细菌PNPase蛋白假定人类对应物的人类基因的鉴定，这表明外泌体虽然确实具有相似的功能活性，但并非细菌降解体的真核等效物。
