Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA 92121, USA.
Mol Cell. 2013 May 9;50(3):344-55. doi: 10.1016/j.molcel.2013.04.001.
Argonaute proteins use small RNAs to guide the silencing of complementary target RNAs in many eukaryotes. Although small RNA biogenesis pathways are well studied, mechanisms for removal of guide RNAs from Argonaute are poorly understood. Here we show that the Argonaute2 (Ago2) guide RNA complex is extremely stable, with a half-life on the order of days. However, highly complementary target RNAs destabilize the complex and significantly accelerate release of the guide RNA from Ago2. This "unloading" activity can be enhanced by mismatches between the target and the guide 5' end and attenuated by mismatches to the guide 3' end. The introduction of 3' mismatches leads to more potent silencing of abundant mRNAs in mammalian cells. These findings help to explain why the 3' ends of mammalian microRNAs (miRNAs) rarely match their targets, suggest a mechanism for sequence-specific small RNA turnover, and offer insights for controlling small RNAs in mammalian cells.
Argonaute 蛋白利用小 RNA 来指导许多真核生物中互补靶 RNA 的沉默。尽管小 RNA 的生物发生途径得到了很好的研究，但 Argonaute 上向导 RNA 的去除机制仍知之甚少。在这里，我们表明 Argonaute2（Ago2）向导 RNA 复合物极其稳定，半衰期约为几天。然而，高度互补的靶 RNA 会使复合物不稳定，并显著加速向导 RNA 从 Ago2 中的释放。这种“卸载”活性可以通过靶标与向导 5'端之间的错配增强，并通过向导 3'端的错配减弱。引入 3' 错配会导致哺乳动物细胞中大量 mRNA 的沉默更为有效。这些发现有助于解释为什么哺乳动物 microRNAs (miRNAs) 的 3' 端很少与它们的靶标匹配，为序列特异性小 RNA 周转提供了一种机制，并为控制哺乳动物细胞中的小 RNA 提供了思路。
