Department of Cell Biology, SUNY Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203, USA.
Nucleic Acids Res. 2011 Jun;39(11):4851-65. doi: 10.1093/nar/gkr045. Epub 2011 Feb 8.
Type 2 internal ribosomal entry sites (IRESs) of encephalomyocarditis virus (EMCV), foot-and-mouth disease virus (FMDV) and other picornaviruses comprise five major domains H-L. Initiation of translation on these IRESs begins with specific binding of the central domain of initiation factor, eIF4G to the J-K domains, which is stimulated by eIF4A. eIF4G/eIF4A then restructure the region of ribosomal attachment on the IRES and promote recruitment of ribosomal 43S pre-initiation complexes. In addition to canonical translation factors, type 2 IRESs also require IRES trans-acting factors (ITAFs) that are hypothesized to stabilize the optimal IRES conformation that supports efficient ribosomal recruitment: the EMCV IRES is stimulated by pyrimidine tract binding protein (PTB), whereas the FMDV IRES requires PTB and ITAF(45). To test this hypothesis, we assessed the effect of ITAFs on the conformations of EMCV and FMDV IRESs by comparing their influence on hydroxyl radical cleavage of these IRESs from the central domain of eIF4G. The observed changes in cleavage patterns suggest that cognate ITAFs promote similar conformational changes that are consistent with adoption by the IRESs of comparable, more compact structures, in which domain J undergoes local conformational changes and is brought into closer proximity to the base of domain I.
2 型内部核糖体进入位点（IRES）的脑心肌炎病毒（EMCV），口蹄疫病毒（FMDV）和其他小核糖核酸病毒由五个主要结构域 H-L 组成。这些 IRES 上的翻译起始是从起始因子的中央结构域与 J-K 结构域的特异性结合开始的，该结合由 eIF4A 刺激。eIF4G/eIF4A 随后重构 IRES 上的核糖体附着区域，并促进核糖体 43S 起始复合物的募集。除了规范的翻译因子外，2 型 IRES 还需要假定能够稳定支持有效核糖体募集的最佳 IRES 构象的 IRES 反式作用因子（ITAF）：EMCV IRES 受嘧啶核苷酸结合蛋白（PTB）刺激，而 FMDV IRES 需要 PTB 和 ITAF(45)。为了检验这一假说，我们通过比较它们对 eIF4G 中央结构域中这些 IRES 的羟基自由基切割的影响，评估了 ITAF 对 EMCV 和 FMDV IRES 构象的影响。观察到的切割模式的变化表明，同源 ITAF 促进相似的构象变化，这与 IRES 采用可比的、更紧凑的结构一致，其中 J 结构域发生局部构象变化并更接近 I 结构域的基部。
