Biochemistry Center Regensburg (BZR), Laboratory for RNA Biology, University of Regensburg, Regensburg 93053, Germany.
Laboratory for RNA Biology and Posttranscriptional Regulation, Berlin Institute for Medical Systems Biology, Max-Delbrück Center for Molecular Medicine, Berlin 13125, Germany.
Mol Cell. 2016 Jul 7;63(1):110-24. doi: 10.1016/j.molcel.2016.05.026. Epub 2016 Jun 23.
The Lupus autoantigen La is an RNA-binding protein that stabilizes RNA polymerase III (Pol III) transcripts and supports RNA folding and has in addition been implicated in the mammalian microRNA (miRNA) pathway. Here, we have analyzed effects of La depletion on Argonaute (Ago)-bound small RNAs in human cells. We find that in the absence of La, distinct tRNA fragments are loaded into Ago proteins. Thus, La functions as gatekeeper ensuring correct tRNA maturation and protecting the miRNA pathway from potentially functional tRNA fragments. However, one specific isoleucin pre-tRNA produces both a functional tRNA and a miRNA even when La is present. We demonstrate that the fully complementary 5' leader and 3' trailer of the pre-tRNA-Ile form a double-stranded RNA molecule that has low affinity to La. Instead, Exportin-5 (Xpo5) recognizes it as miRNA precursor and transports it into the cytoplasm for Dicer processing and Ago loading.
狼疮自身抗原 La 是一种 RNA 结合蛋白，可稳定 RNA 聚合酶 III（Pol III）转录本，并支持 RNA 折叠，此外还与哺乳动物 microRNA（miRNA）途径有关。在这里，我们分析了 La 耗竭对人细胞中 Argonaute（Ago）结合的小 RNA 的影响。我们发现，在没有 La 的情况下，不同的 tRNA 片段被加载到 Ago 蛋白中。因此，La 作为守门员发挥作用，确保正确的 tRNA 成熟，并保护 miRNA 途径免受潜在功能的 tRNA 片段的影响。然而，即使存在 La，一种特定的异亮氨酸前 tRNA 也会产生功能性 tRNA 和 miRNA。我们证明，前 tRNA-Ile 的完全互补 5' 引导序列和 3' 尾随序列形成了一种与 La 亲和力低的双链 RNA 分子。相反，Exportin-5（Xpo5）将其识别为 miRNA 前体，并将其运送到细胞质中进行 Dicer 加工和 Ago 加载。
