Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, China.
Wellcome Cancer Research UK Gurdon Institute, University of Cambridge, Cambridge CB2 1QN, United Kingdom; Department of Genetics, University of Cambridge, Cambridge CB2 3EH, United Kingdom.
Genes Dev. 2019 Jan 1;33(1-2):90-102. doi: 10.1101/gad.319293.118. Epub 2018 Dec 19.
Piwi-interacting RNAs (piRNAs) engage Piwi proteins to suppress transposons and nonself nucleic acids and maintain genome integrity and are essential for fertility in a variety of organisms. In , most piRNA precursors are transcribed from two genomic clusters that contain thousands of individual piRNA transcription units. While a few genes have been shown to be required for piRNA biogenesis, the mechanism of piRNA transcription remains elusive. Here we used functional proteomics approaches to identify an upstream sequence transcription complex (USTC) that is essential for piRNA biogenesis. The USTC contains piRNA silencing-defective 1 (PRDE-1), SNPC-4, twenty-one-U fouled-up 4 (TOFU-4), and TOFU-5. The USTC forms unique piRNA foci in germline nuclei and coats the piRNA cluster genomic loci. USTC factors associate with the Ruby motif just upstream of type I piRNA genes. USTC factors are also mutually dependent for binding to the piRNA clusters and forming the piRNA foci. Interestingly, USTC components bind differentially to piRNAs in the clusters and other noncoding RNA genes. These results reveal the USTC as a striking example of the repurposing of a general transcription factor complex to aid in genome defense against transposons.
Piwi 相互作用 RNA（piRNAs）与 Piwi 蛋白结合，抑制转座子和非自身核酸，维持基因组完整性，对于各种生物体的生殖能力至关重要。在 ，大多数 piRNA 前体是从包含数千个单独 piRNA 转录单元的两个基因组簇转录而来的。虽然已经证明有几个基因对于 piRNA 的生物发生是必需的，但 piRNA 转录的机制仍然难以捉摸。在这里，我们使用功能蛋白质组学方法来鉴定一个对于 piRNA 生物发生至关重要的上游序列转录复合物（USTC）。USTC 包含 piRNA 沉默缺陷 1（PRDE-1）、SNPC-4、二十一个-U 搞砸 4（TOFU-4）和 TOFU-5。USTC 在生殖细胞核中形成独特的 piRNA 焦点，并覆盖 piRNA 簇基因组位置。USTC 因子与 I 型 piRNA 基因上游的 Ruby 基序结合。USTC 因子之间也相互依赖，以结合 piRNA 簇并形成 piRNA 焦点。有趣的是，USTC 成分与簇中的 piRNAs 和其他非编码 RNA 基因的结合存在差异。这些结果揭示了 USTC 作为一个引人注目的例子，说明了一般转录因子复合物的重新利用有助于抵御转座子的基因组防御。
