PLoS Genet∣RNA結合蛋白HOS5參與前體mRNA剪接的機制研究

今天是一篇關於RNA結合蛋白HOS5參與前體mRNA剪接的研究。

題目為：A KH-Domain RNA-Binding Protein Interacts with FIERY2/CTD Phosphatase-Like 1 and Splicing Factors and Is Important for Pre-mRNA Splicing in Arabidopsis

主要內容為：含有KH結構域的RNA結合蛋白HOS5可以與FRY2/CPL1互作，也可以與剪接因子RS40和RS41互作，調控前體mRNA的剪接，尤其在逆境條件下發揮作用。

前體mRNA加工包括5加帽，剪接和3聚腺苷酸化，這些對基因表達至關重要，並且與轉錄緊密聯繫。RNA聚合酶II（RNAP II）的磷酸化C末端結構域（CTD）可作為前體mRNA加工因子募集的平台，但其他參與招募的組分還不清楚。在擬南芥脅迫信號轉導的遺傳學研究中，我們分離了一個KH結構域RNA結合蛋白HOS5，在逆境基因調控和脅迫耐受中起重要作用。文章作者發現，HOS5與FRY2/CPL1相互作用，它們在核斑點中也與兩個新的剪接因子RS40和RS41相互作用。在fry2突變體中，HOS5不能被募集到核斑點，而是主要定位在核質中。這些基因的突變體具有類似的逆境敏感表型。在鹽脅迫條件下，轉錄組分析鑒定了這些突變體中許多與脅迫相關的基因，有顯著的內含子保留。本文的研究顯示，除了RNAP II，CTD磷酸酶還可以募集特定的剪接因子和RNA結合蛋白，來調節某些轉錄本的共轉錄，以適應環境脅迫。

摘要：

真核生物基因組編碼數以百計的RNA結合蛋白，但大多數這些蛋白質的功能是未知的。在擬南芥脅迫信號轉導的遺傳研究中，我們鑒定了一個KH結構域RNA結合蛋白HOS5，其在逆境基因調控和脅迫耐受中是所需的。HOS5在體外和體內均與FRY2/CPL1互作。這種互作由FRY2/CPL1的第一個雙鏈RNA結合結構域和HOS5的KH結構域介導。有趣的是，HOS5和FRY2/CPL1也與兩個新的富含絲氨酸-精氨酸（SR）的剪接因子RS40和RS41在核散斑中互作。重要的是，FRY2/CPL1對於HOS5募集是必需的。在fry2突變體中，HOS5無法定位於核斑點，但主要定位於核質。hos5突變體在mRNA輸出中受損，並且在細胞核中積累了大量的mRNA，特別是在鹽脅迫條件下。所有這些基因的擬南芥突變體表現出類似的逆境敏感表型。這些突變體的RNA-seq分析發現，在鹽脅迫下在許多脅迫相關基因中，檢測到顯著的內含子保留，而在正常條件下沒有。本研究不僅鑒定了幾種新的前體mRNA加工的調節因子，它們對植物脅迫反應具有重要作用；而且還提出，除了RNAP II CTD外，FRY2/CPL1也可能募集特定的因子來調節某些轉錄本的共轉錄，以應對環境的挑戰。

Abstract：

Eukaryotic genomes encode hundreds of RNA-binding proteins, yet the functions of most of these proteins are unknown. In a genetic study of stress signal transduction in Arabidopsis, we identified a K homology (KH)-domain RNA-binding protein, HOS5 (High Osmotic Stress Gene Expression 5), as required for stress gene regulation and stress tolerance. HOS5 was found to interact with FIERY2/RNA polymerase II (RNAP II) carboxyl terminal domain (CTD) phosphatase-like 1 (FRY2/CPL1) both in vitro and in vivo. This interaction is mediated by the first double-stranded RNA-binding domain of FRY2/CPL1 and the KH domains of HOS5. Interestingly, both HOS5 and FRY2/CPL1 also interact with two novel serine-arginine (SR)-rich splicing factors, RS40 and RS41, in nuclear speckles. Importantly, FRY2/CPL1 is required for the recruitment of HOS5. In fry2 mutants, HOS5 failed to be localized in nuclear speckles but was found mainly in the nucleoplasm. hos5 mutants were impaired in mRNA export and accumulated a significant amount of mRNA in the nuclei, particularly under salt stress conditions. Arabidopsis mutants of all these genes exhibit similar stress-sensitive phenotypes. RNA-seq analyses of these mutants detected significant intron retention in many stress-related genes under salt stress but not under normal conditions. Our study not only identified several novel regulators of pre-mRNA processing as important for plant stress response but also suggested that, in addition to RNAP II CTD that is a well-recognized platform for the recruitment of mRNA processing factors, FRY2/CPL1 may also recruit specific factors to regulate the co-transcriptional processing of certain transcripts to deal with environmental challenges.

Figure 3. HOS5 interacts with FRY2 and two RS proteins