The h subunit of eIF3 promotes reinitiation competence during translation of mRNAs harboring upstream open reading frames
The h subunit of eIF3 promotes reinitiation competence during translation of mRNAs harboring upstream open reading frames
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DOI：
10.1261/rna.2056010
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发表时间：
2010-04-01
期刊：
影响因子：
4.5
通讯作者：
Von Arnim, Albrecht G.
中科院分区：
文献类型：
--
作者：
Roy, Bijoyita;Vaughn, Justin N.;Von Arnim, Albrecht G.
上游开放阅读框 (uORF) 是信使 RNA 5' 前导序列中的蛋白质编码元件。 uORF 通常会抑制主 ORF 的翻译，因为执行翻译延伸的核糖体会永久或有条件地丧失重新启动能力。有条件丧失后，至少可以通过重新获得新鲜的甲硫氨酰-tRNA来恢复重新启动能力。拟南芥真核起始因子 3 (eIF3) 的保守 h 亚基可减轻某些 uORF 的抑制作用。在这里，我们通过将拟南芥 AtbZip11 (At4g34590) 和酵母 GCN4 突变 5' 前导序列的基因表达数据与野生型和 eif3h 突变植物中翻译起始的计算模型相结合，更精确地定义了这种情况是如何发生的。 AtbZip11 中四个系统发育保守的 uORF 中，三个对翻译具有抑制作用，而一个则具有抗抑制作用。 eIF3h 中的突变对 uORF 起始密码子识别没有重大影响。相反，eIF3h 支持 uORF 翻译后有效的重新启动。建模表明，uORF 翻译过程中重新启动能力的永久丧失在突变体中发生的速度比野生型更快。因此，eIF3h 确保一小部分 uORF 翻译核糖体保留其恢复扫描的能力。使用酵母 GCN4 前导序列的实验没有提供 eIF3h 促进 tRNA 重新获取的证据。总之，这些结果将翻译起始中的特定分子功能归因于多细胞真核生物中的单个 eIF3 亚基。
Upstream open reading frames (uORFs) are protein coding elements in the 5' leader of messenger RNAs. uORFs generally inhibit translation of the main ORF because ribosomes that perform translation elongation suffer either permanent or conditional loss of reinitiation competence. After conditional loss, reinitiation competence may be regained by, at the minimum, reacquisition of a fresh methionyl-tRNA. The conserved h subunit of Arabidopsis eukaryotic initiation factor 3 (eIF3) mitigates the inhibitory effects of certain uORFs. Here, we define more precisely how this occurs, by combining gene expression data from mutated 5' leaders of Arabidopsis AtbZip11 (At4g34590) and yeast GCN4 with a computational model of translation initiation in wild-type and eif3h mutant plants. Of the four phylogenetically conserved uORFs in AtbZip11, three are inhibitory to translation, while one is anti-inhibitory. The mutation in eIF3h has no major effect on uORF start codon recognition. Instead, eIF3h supports efficient reinitiation after uORF translation. Modeling suggested that the permanent loss of reinitiation competence during uORF translation occurs at a faster rate in the mutant than in the wild type. Thus, eIF3h ensures that a fraction of uORF-translating ribosomes retain their competence to resume scanning. Experiments using the yeast GCN4 leader provided no evidence that eIF3h fosters tRNA reaquisition. Together, these results attribute a specific molecular function in translation initiation to an individual eIF3 subunit in a multicellular eukaryote.