Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232-0146, USA; Center for Structural Biology, Vanderbilt University School of Medicine, Nashville, TN 37232-0146, USA.
Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9039, USA.
Cell Rep. 2023 Aug 29;42(8):112988. doi: 10.1016/j.celrep.2023.112988. Epub 2023 Aug 14.
mRNA in eukaryotic cells is packaged into highly compacted ribonucleoprotein particles (mRNPs) in the nucleus and exported to the cytoplasm for translation. mRNP packaging and export require the evolutionarily conserved transcription-export (TREX) complex. TREX facilitates loading of various RNA-binding proteins on mRNA through the action of its DDX39B subunit. SARNP (Tho1 [transcriptional defect of Hpr1 by overexpression 1] in yeast) is shown to interact with DDX39B and affect mRNA export. The molecular mechanism of how SARNP recognizes DDX39B and functions in mRNP assembly is unclear. Here, we determine the crystal structure of a Tho1/DDX39B/RNA complex, revealing a multivalent interaction mediated by tandem DDX39B interacting motifs in SARNP/Tho1. The high-order complex of SARNP and DDX39B is evolutionarily conserved, and human SARNP can engage with five DDX39B molecules. RNA sequencing (RNA-seq) from SARNP knockdown cells shows the most affected RNAs in export are GC rich. Our work suggests the role of the high-order SARNP/DDX39B/RNA complex in mRNP assembly and export.
真核细胞中的 mRNA 在细胞核中被包装成高度紧凑的核糖核蛋白颗粒（mRNP），并被输出到细胞质中进行翻译。mRNP 的包装和输出需要进化上保守的转录-输出（TREX）复合物。TREX 通过其 DDX39B 亚基的作用促进各种 RNA 结合蛋白在 mRNA 上的加载。SARNP（酵母中的 Tho1[通过过表达 Hpr1 转录缺陷 1]）被证明与 DDX39B 相互作用并影响 mRNA 输出。SARNP 如何识别 DDX39B 并在 mRNP 组装中发挥作用的分子机制尚不清楚。在这里，我们确定了 Tho1/DDX39B/RNA 复合物的晶体结构，揭示了串联 DDX39B 相互作用基序在 SARNP/Tho1 中介导的多价相互作用。SARNP 和 DDX39B 的高阶复合物在进化上是保守的，并且人 SARNP 可以与五个 DDX39B 分子结合。SARNP 敲低细胞的 RNA 测序（RNA-seq）显示，受影响最大的 RNA 是 GC 丰富的。我们的工作表明，高阶 SARNP/DDX39B/RNA 复合物在 mRNP 组装和输出中的作用。
