PCI domain proteins play important roles in post-transcriptional gene regulation. In the TREX-2 complex, PCI domain-containing Sac3 and Thp1 proteins and accessory Sem1 protein form a ternary complex required for mRNA nuclear export. In contrast, structurally related Thp3–Csn12–Sem1 complex mediates pre-mRNA splicing. In this study, we determined the structure of yeast Thp3186–470–Csn12–Sem1 ternary complex at 2.9 Å resolution. Both Thp3 and Csn12 structures have a typical PCI structural fold, characterized by a stack of α-helices capped by a C-terminal winged-helix (WH) domain. The overall structure of Thp3186–470–Csn12–Sem1 complex has an inverted V-shape with Thp3 and Csn12 forming the two sides. A fishhook-shaped Sem1 makes extensive contacts on Csn12 to stabilize its conformation. The overall structure of Thp3186–470–Csn12–Sem1 complex resembles the previously reported Sac3–Thp1–Sem1 complex, but also has significant structural differences. The C-terminal WH domains of Thp3 and Csn12 form a continuous surface to bind different forms of nucleic acids with micromolar affinity. Mutation of the basic residues in the WH domains of Thp3 and Csn12 affects nucleic acid binding in vitro and mRNA splicing in vivo. The Thp3–Csn12–Sem1 structure provides a foundation for further exploring the structural elements required for its specific recruitment to spliceosome for pre-mRNA splicing.

中文翻译：

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在 mRNA 剪接中起作用的核酸结合 Thp3-Csn12-Sem1 复合物的结构组装

PCI结构域蛋白在转录后基因调控中发挥重要作用。在 TREX-2 复合物中，含有 PCI 结构域的 Sac3 和 Thp1 蛋白和辅助 Sem1 蛋白形成 mRNA 核输出所需的三元复合物。相反，结构相关的 Thp3-Csn12-Sem1 复合物介导前 mRNA 剪接。在这项研究中，我们以 2.9 Å 的分辨率确定了酵母 Thp3186–470–Csn12–Sem1 三元复合物的结构。Thp3 和 Csn12 结构都具有典型的 PCI 结构折叠，其特征在于由 C 端翼螺旋 (WH) 结构域覆盖的一堆 α-螺旋。Thp3186-470-Csn12-Sem1复合物的整体结构呈倒V形，Thp3和Csn12形成两侧。鱼钩形 Sem1 在 Csn12 上进行广泛接触以稳定其构象。Thp3186-470-Csn12-Sem1 复合物的整体结构类似于先前报道的 Sac3-Thp1-Sem1 复合物，但也存在显着的结构差异。Thp3 和 Csn12 的 C 末端 WH 结构域形成一个连续表面，以微摩尔亲和力结合不同形式的核酸。Thp3 和 Csn12 的 WH 结构域中碱性残基的突变影响体外核酸结合和体内 mRNA 剪接。Thp3-Csn12-Sem1 结构为进一步探索其特异性募集到剪接体进行前 mRNA 剪接所需的结构元件提供了基础。Thp3 和 Csn12 的 WH 结构域中碱性残基的突变影响体外核酸结合和体内 mRNA 剪接。Thp3-Csn12-Sem1 结构为进一步探索其特异性募集到剪接体进行前 mRNA 剪接所需的结构元件提供了基础。Thp3 和 Csn12 的 WH 结构域中碱性残基的突变影响体外核酸结合和体内 mRNA 剪接。Thp3-Csn12-Sem1 结构为进一步探索其特异性募集到剪接体进行前 mRNA 剪接所需的结构元件提供了基础。