On the functions of the h subunit of eukaryotic initiation factor 3 in late stages of translation initiation.
On the functions of the h subunit of eukaryotic initiation factor 3 in late stages of translation initiation.
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DOI：
10.1186/gb-2007-8-4-r60
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发表时间：
2007
期刊：
影响因子：
12.3
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中科院分区：
文献类型：
--
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报告基因转基因检测和比较多核糖体微阵列分析表明，完整的h亚基拟南芥eIF3有助于有效的翻译起始的mRNA前导序列窝藏多个uORF。真核生物翻译起始因子3（eIF3）在胞质mRNA翻译起始过程中具有多种作用。然而，eIF3的各个亚基如何促进特定mRNA的翻译仍然知之甚少。这对于在芽殖酵母中不保守的那些亚基（例如eIF3h）尤其如此。在拟南芥突变体中使用稳定的报告转基因，证明eIF 3的h亚基有助于在其5'前导序列中含有上游开放阅读框（uORF）的mRNA的有效翻译起始。uORF作为一种翻译调控机制，存在于30%以上的拟南芥mRNA中，并在转录调控因子和蛋白质修饰酶的mRNA中富集。在野生型和eif3h突变体幼苗中多核糖体加载的微阵列比较显示，eIF3h通常有助于维持携带多个uORF的mRNA的有效多核糖体加载。然而，此外，eIF3h还增强了具有长前导序列或编码序列的mRNA的多核糖体负载。此外，在eif3h突变体中，某些mRNA功能组（包括核糖体蛋白）的相对多核糖体负载实际上增加，这表明翻译控制的调节子可以通过通用翻译起始因子的突变来揭示。完整的eIF3h蛋白有助于在含有多个uORF的5'前导序列上的有效翻译起始，尽管也涉及不依赖于uORF的mRNA特征。
Reporter transgene assays and comparative polysome-microarray analysis reveal that the intact h subunit of Arabidopsis eIF3 contributes to efficient translation initiation on mRNA leader sequences harbouring multiple uORFs. The eukaryotic translation initiation factor 3 (eIF3) has multiple roles during the initiation of translation of cytoplasmic mRNAs. How individual subunits of eIF3 contribute to the translation of specific mRNAs remains poorly understood, however. This is true in particular for those subunits that are not conserved in budding yeast, such as eIF3h. Working with stable reporter transgenes in Arabidopsis thaliana mutants, it was demonstrated that the h subunit of eIF3 contributes to the efficient translation initiation of mRNAs harboring upstream open reading frames (uORFs) in their 5' leader sequence. uORFs, which can function as devices for translational regulation, are present in over 30% of Arabidopsis mRNAs, and are enriched among mRNAs for transcriptional regulators and protein modifying enzymes. Microarray comparisons of polysome loading in wild-type and eif3h mutant seedlings revealed that eIF3h generally helps to maintain efficient polysome loading of mRNAs harboring multiple uORFs. In addition, however, eIF3h also boosted the polysome loading of mRNAs with long leaders or coding sequences. Moreover, the relative polysome loading of certain functional groups of mRNAs, including ribosomal proteins, was actually increased in the eif3h mutant, suggesting that regulons of translational control can be revealed by mutations in generic translation initiation factors. The intact eIF3h protein contributes to efficient translation initiation on 5' leader sequences harboring multiple uORFs, although mRNA features independent of uORFs are also implicated.