Small regulatory RNAs such as siRNAs and piRNAs regulate splicing, transcription, and genome integrity in many eukaryotes. In C. elegans, siRNAs bind nuclear Argonautes (AGOs), which interact with homologous pre-mRNAs to recruit downstream silencing effectors such as NRDE-2 to direct co-transcriptional gene silencing (cTGS or nuclear RNAi). To further our understanding of the mechanism of nuclear RNAi, we conducted IP-Mass Spectrometry on C. elegans NRDE-2. The major NRDE-2 interacting protein identified was the RNA helicase MTR-4. co-IP analyses confirmed a physical association between NRDE-2 and MTR-4. MTR-4 co-localizes with NRDE-2 within the nuclei of most/all C. elegans somatic and germline cells. MTR-4 is required for nuclear RNAi, and interestingly, MTR-4 is recruited to pre-mRNAs undergoing nuclear RNAi via a process requiring nuclear siRNAs, the nuclear AGO HRDE-1, and NRDE-2, indicating that MTR-4 is a component of the C. elegans nuclear RNAi machinery. Finally, we confirm previous reports showing that mammalian HsNRDE2 and HsMTR4 also physically interact. Our data show that the NRDE-2/MTR-4 interactions are evolutionarily conserved and that, in C. elegans, the NRDE-2/MTR-4 complex contributes to siRNA-directed co-transcriptional gene silencing.

中文翻译：

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保守的 NRDE-2/MTR-4 复合物介导秀丽隐杆线虫的核 RNAi。

siRNA 和 piRNA 等小调节 RNA 调节许多真核生物中的剪接、转录和基因组完整性。在秀丽隐杆线虫中，siRNA 结合核 Argonautes (AGO)，后者与同源前 mRNA 相互作用，招募下游沉默效应子（如 NRDE-2）来指导共转录基因沉默（cTGS 或核 RNAi）。为了进一步了解核 RNAi 的机制，我们对秀丽隐杆线虫 NRDE-2 进行了 IP 质谱分析。鉴定出的主要 NRDE-2 相互作用蛋白是 RNA 解旋酶 MTR-4。co-IP 分析证实了 NRDE-2 和 MTR-4 之间的物理关联。MTR-4 与 NRDE-2 共定位于大多数/所有秀丽隐杆线虫体细胞和生殖细胞的细胞核内。MTR-4 是核 RNAi 所必需的，有趣的是，MTR-4 通过需要核 siRNA、核 AGO HRDE-1 和 NRDE-2 的过程被招募到进行核 RNAi 的前 mRNA，这表明 MTR-4 是一种线虫核 RNAi 机制的组成部分。最后，我们证实了之前的报告，表明哺乳动物 HsNRDE2 和 HsMTR4 也存在物理相互作用。我们的数据表明，NRDE-2/MTR-4 相互作用在进化上是保守的，并且在线虫中，NRDE-2/MTR-4 复合物有助于 siRNA 指导的共转录基因沉默。