RNA G-quadruplex (rG4) structures can influence the fate and functions of mRNAs, especially the translation process. The presence of rG4 structures in 5′-untranslated regions (5′-UTRs) of mRNAs generally represses translation. However, rG4 structures can also promote internal ribosome entry site (IRES)-mediated translation as one of its determinants. Here, we report the identification of an evolutionary conserved rG4-forming sequence motif at the extreme 5′-end of the unusually long 5′-UTR (1.7 kb) in the transcript of human cIAP1 gene encoding the cellular inhibitor of apoptosis protein-1 that promotes cell survival by suppressing apoptosis and is overexpressed in various cancer cells. Expectedly, NMR study, CD spectroscopy, and UV melting assay confirm the formation of a potassium ion-dependent intramolecular and parallel rG4 structure at the sequence stretch. Moreover, the G4-RNA-specific precipitation using biotin-linked biomimetic BioCyTASQ validates the formation of the rG4 structure in the cIAP1 5′-UTR in cells. Interestingly, disruption of the rG4 structure in the cIAP1 5′-UTR results in a dramatic reduction in translation of the downstream luciferase reporter in cells, suggesting a translation-promoting effect of the rG4 structure, contrary to many earlier reports. Furthermore, enhancement of translation by the cIAP1 rG4 structure occurs in an IRES-independent manner.

中文翻译：

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人类 cIAP1 mRNA 5′-UTR 中的稳定 RNA G-四链体以不依赖于 IRES 的方式促进翻译

RNA G 四链体 (rG4) 结构可以影响 mRNA 的命运和功能，尤其是翻译过程。mRNA 5'-非翻译区 (5'-UTR) 中 rG4 结构的存在通常会抑制翻译。然而，rG4 结构也可以促进内部核糖体进入位点 (IRES) 介导的翻译，这是其决定因素之一。在这里，我们报告了在编码细胞凋亡蛋白-1的细胞抑制剂的人cIAP1基因转录本中异常长的5'-UTR（1.7 kb）的最5'端鉴定了进化保守的rG4形成序列基序。通过抑制细胞凋亡来促进细胞存活，并在各种癌细胞中过度表达。预计，NMR 研究、CD 光谱和 UV 熔解测定证实在序列延伸处形成了钾离子依赖性分子内平行 rG4 结构。此外，使用生物素连接的仿生 BioCyTASQ 进行的 G4-RNA 特异性沉淀验证了细胞中cIAP1 5'-UTR中 rG4 结构的形成。有趣的是， cIAP1 5'-UTR中 rG4 结构的破坏导致细胞中下游荧光素酶报告基因的翻译急剧减少，这表明 rG4 结构具有翻译促进作用，这与许多早期报道相反。此外，cIAP1 rG4 结构对翻译的增强以不依赖于 IRES 的方式发生。