The pre-mRNA splicing and transcription factor Tat-SF1 is a functional partner of the spliceosome SF3b1 subunit via a U2AF homology motif interface
The pre-mRNA splicing and transcription factor Tat-SF1 is a functional partner of the spliceosome SF3b1 subunit via a U2AF homology motif interface
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DOI：
10.1074/jbc.ra118.006764
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发表时间：
2019-02-22
影响因子：
4.8
通讯作者：
Kielkopf, Clara L.
中科院分区：
文献类型：
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作者：
Loerch, Sarah;Leach, Justin R.;Kielkopf, Clara L.
转录延长和前mRNA剪接因子TAT-SF1与剪接体的U2小核核糖核蛋白(SnRNP)相关。然而，介导TAT-SF1-U2 SnRNP关联的直接结合伙伴和潜在相互作用仍不清楚。在这里，我们确定SF3B1是U2SnRNP的TAT-SF1相互作用亚基。我们的1.1A分辨率晶体结构表明，TAT-SF1含有一个U2AF同源基序(UHM)蛋白质-蛋白质相互作用模块。我们证明了与其他含有U2AF配体基序(ULM)的剪接因子相比，TAT-SF1优先和直接结合SF3B1亚基，并进一步证实SF3B1的结合依赖于TAT-SF1 UHM的完整性。接下来，我们比较了五个已知SF3B1ULM的TAT-SF1结合亲和力，然后分别在1.9A和2.1A分辨率下确定了具有代表性的高亲和力和低亲和力的SF3B1ULM与TAT-SF1UHM的结构。这些结构揭示了典型的UHM-ULM界面，包括ULM色氨酸(SF3B1 TRP(338))的TAT-SF1结合口袋以及与基本ULM尾部的静电相互作用。重要的是，我们发现SF3B1调节TAT-SF1的水平，这两个因素影响重叠的代表性转录本的表达，这与TAT-SF1和SF3B1的功能伙伴关系一致。综上所述，这些结果定义了TAT-SF1-U2 SnRNP复合体用于基因调控的新的分子界面。
The transcription elongation and pre-mRNA splicing factor Tat-SF1 associates with the U2 small nuclear ribonucleoprotein (snRNP) of the spliceosome. However, the direct binding partner and underlying interactions mediating the Tat-SF1-U2 snRNP association remain unknown. Here, we identified SF3b1 as a Tat-SF1-interacting subunit of the U2 snRNP. Our 1.1 A resolution crystal structure revealed that Tat-SF1 contains a U2AF homology motif (UHM) protein-protein interaction module. We demonstrated that Tat-SF1 preferentially and directly binds the SF3b1 subunit compared with other U2AF ligand motif (ULM)-containing splicing factors, and further established that SF3b1 association depends on the integrity of the Tat-SF1 UHM. We next compared the Tat-SF1-binding affinities for each of the five known SF3b1 ULMs and then determined the structures of representative high- and low-affinity SF3b1 ULM complexes with the Tat-SF1 UHM at 1.9 A and 2.1 A resolutions, respectively. These structures revealed a canonical UHM-ULM interface, comprising a Tat-SF1 binding pocket for a ULM tryptophan (SF3b1 Trp(338)) and electrostatic interactions with a basic ULM tail. Importantly, we found that SF3b1 regulates Tat-SF1 levels and that these two factors influence expression of overlapping representative transcripts, consistent with a functional partnership of Tat-SF1 and SF3b1. Altogether, these results define a new molecular interface of the Tat-SF1-U2 snRNP complex for gene regulation.