Bhattacharjee Sayan, Abaeva Irina S, Brown Zuben P, Arhab Yani, Fallah Hengameh, Hellen Christopher U T, Frank Joachim, Pestova Tatyana V
bioRxiv. 2025 Jun 11:2025.06.11.659010. doi: 10.1101/2025.06.11.659010.
The encephalomyocarditis virus (EMCV) IRES and other Type 2 IRESs comprise domains H-L and specifically interact with eIF4G/eIF4A through their essential JK domain. However, the JK domain is not sufficient for IRES function, which also requires the preceding domain I of unknown function. To identify interactions that drive ribosomal recruitment of eIF4G/eIF4A-bound Type 2 IRESs, we determined the cryo-EM structure of 48S initiation complexes formed on the EMCV IRES. It revealed that the apical domain I cloverleaf contacts ribosomal proteins uS13 and uS19 via its Id subdomain and that the essential GNRA tetraloop in subdomain Ic interacts directly with the TψC domain of initiator tRNA. Functional assays supported the exceptional role of these interactions for initiation on this IRES. The strong conservation of primary and secondary structures of the apex of domain I among Type 2 IRESs suggests that the reported interactions are a common essential feature of them all.
脑心肌炎病毒（EMCV）内部核糖体进入位点（IRES）和其他2型IRES包含H-L结构域，并通过其关键的JK结构域与真核起始因子4G（eIF4G）/真核起始因子4A（eIF4A）特异性相互作用。然而，JK结构域不足以实现IRES功能，IRES功能还需要前面功能未知的结构域I。为了确定驱动与eIF4G/eIF4A结合的2型IRES核糖体募集的相互作用，我们确定了在EMCV IRES上形成的48S起始复合物的冷冻电镜结构。结果显示，顶端结构域I的三叶草结构通过其Id亚结构域与核糖体蛋白uS13和uS19接触，并且结构域Ic中的关键GNRA四环直接与起始tRNA的TψC结构域相互作用。功能分析支持了这些相互作用在该IRES起始过程中的特殊作用。2型IRES中结构域I顶端的一级和二级结构的高度保守表明，所报道的相互作用是它们共有的关键特征。
