Trypanosoma brucei Translation Initiation Factor Homolog EIF4E6 Forms a Tripartite Cytosolic Complex with EIF4G5 and a Capping Enzyme Homolog
Trypanosoma brucei Translation Initiation Factor Homolog EIF4E6 Forms a Tripartite Cytosolic Complex with EIF4G5 and a Capping Enzyme Homolog
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DOI：
10.1128/ec.00071-14
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发表时间：
2014-07-01
期刊：
影响因子：
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通讯作者：
Campbell, David A.
中科院分区：
文献类型：
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作者：
Freire, Eden R.;Malvezzi, Amaranta M.;Campbell, David A.
锥虫缺乏大多数真核生物的转录控制特征，其由一个基因一个启动子排列的基因特异性启动子介导。相反，它们的基因组在大的多顺反子中转录，没有明显的功能连锁。因此，基因表达的转录后调控在这些生物体中必须发挥更大的作用。eIF 4 E同源物TbEIF 4 E6在体外结合mRNA帽类似物，并且是可以实现这种作用的体内复合物的一部分。敲低标记有蛋白A-烟草蚀纹病毒蛋白酶切割位点-蛋白C的TbEIF 4 E6至正常表达水平的约15%，导致活细胞显示出一组与鞭毛从细胞体长度脱离相关的表型，如果不是完全的鞭毛损失的话。虽然这些细胞在静止液体培养条件下表现正常，但标准离心导致鞭毛脱离显著增加。此外，TbEIF 4 E6缺失的细胞参与社会运动的能力降低。TbEIF 4 E6蛋白形成含有蛋白三联体的胞质复合物，包括eIF 4G同源物TbEIF 4G 5和称为TbG 5-IP的70.3kDa的假设蛋白。TbG 5-IP分析揭示了两个结构域与预测的二级结构保守的mRNA加帽酶：核苷三磷酸水解酶和鸟苷酰转移酶。这些复合体成员具有通过TbEIF 4 E6和TbG 5-IP的5'帽结构或通过TbEIF 4G 5中的RNA结合结构域进行RNA相互作用的潜力。相关的蛋白质为未来的研究提供了一个路标，以确定这种复合物如何影响加帽的RNA分子。
Trypanosomes lack the transcriptional control characteristic of the majority of eukaryotes that is mediated by gene-specific promoters in a one-gene-one-promoter arrangement. Rather, their genomes are transcribed in large polycistrons with no obvious functional linkage. Posttranscriptional regulation of gene expression must thus play a larger role in these organisms. The eIF4E homolog TbEIF4E6 binds mRNA cap analogs in vitro and is part of a complex in vivo that may fulfill such a role. Knockdown of TbEIF4E6 tagged with protein A-tobacco etch virus protease cleavage site-protein C to approximately 15% of the normal expression level resulted in viable cells that displayed a set of phenotypes linked to detachment of the flagellum from the length of the cell body, if not outright flagellum loss. While these cells appeared and behaved as normal under stationary liquid culture conditions, standard centrifugation resulted in a marked increase in flagellar detachment. Furthermore, the ability of TbEIF4E6-depleted cells to engage in social motility was reduced. The TbEIF4E6 protein forms a cytosolic complex containing a triad of proteins, including the eIF4G homolog TbEIF4G5 and a hypothetical protein of 70.3 kDa, referred to as TbG5-IP. The TbG5-IP analysis revealed two domains with predicted secondary structures conserved in mRNA capping enzymes: nucleoside triphosphate hydrolase and guanylyltransferase. These complex members have the potential for RNA interaction, either via the 5' cap structure for TbEIF4E6 and TbG5-IP or through RNA-binding domains in TbEIF4G5. The associated proteins provide a signpost for future studies to determine how this complex affects capped RNA molecules.