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RNA 干涉 (RNAi)是从真菌到人类都保留下来的一个基因沉默机制。高吞吐量的测序方法表明，动物和植物有大量的小非编码RNA，其中很多的功能仍未确定。尽管RNAi通道具有保守性，但相似类型的小RNA是否在低等真核细胞中也存在却基本上没有人探索过。 现在，人们在丝状菌“脉孢菌”中发现了新的一类小RNA。因其与Argonaute蛋白QDE-2的联系，它们被命名为qiRNAs。同QDE-2一样，它们的出现也是为了响应DNA损伤。它们的长度约为20个核苷酸，比“脉孢菌”的siRNA稍短一些。“脉孢菌”的siRNA突变体对DNA损伤的敏感度增加，表明qiRNAs作为蛋白翻译的抑制因子在DNA修复中扮演一个角色。 本期封面所示为排列成玫瑰花饰形的一组“脉孢菌”子囊，它们具有发荧光的双核囊孢子（由GFP-histone H1来指示）。 推荐原始出处： Nature 459, 274-277 (14 May 2009) | doi:10.1038/nature08041 qiRNA is a new type of small interfering RNA induced by DNA damage Heng-Chi Lee1, Shwu-Shin Chang1, Swati Choudhary1, Antti P. Aalto2, Mekhala Maiti1,3, Dennis H. Bamford2 & Yi Liu1 1 Department of Physiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390, USA 2 Institute of Biotechnology and Department of Biological and Environmental Sciences, Biocenter 2, PO Box 56, FIN-00014 University of Helsinki, Helsinki, Finland 3 Present address: Department of Cell Biology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390, USA. RNA interference pathways use small RNAs to mediate gene silencing in eukaryotes. In addition to small interfering RNAs (siRNAs) and microRNAs, several types of endogenously produced small RNAs have important roles in gene regulation, germ cell maintenance and transposon silencing1, 2, 3, 4. The production of some of these RNAs requires the synthesis of aberrant RNAs (aRNAs) or pre-siRNAs, which are specifically recognized by RNA-dependent RNA polymerases to make double-stranded RNA. The mechanism for aRNA synthesis and recognition is largely unknown. Here we show that DNA damage induces the expression of the Argonaute protein QDE-2 and a new class of small RNAs in the filamentous fungus Neurospora crassa. This class of small RNAs, known as qiRNAs because of their interaction with QDE-2, are about 20–21 nucleotides long (several nucleotides shorter than Neurospora siRNAs), with a strong preference for uridine at the 5' end, and originate mostly from the ribosomal DNA locus. The production of qiRNAs requires the RNA-dependent RNA polymerase QDE-1, the Werner and Bloom RecQ DNA helicase homologue QDE-3 and dicers. qiRNA biogenesis also requires DNA-damage-induced aRNAs as precursors, a process that is dependent on both QDE-1 and QDE-3. Notably, our results suggest that QDE-1 is the DNA-dependent RNA polymerase that produces aRNAs. Furthermore, the Neurospora RNA interference mutants show increased sensitivity to DNA damage, suggesting a role for qiRNAs in the DNA-damage response by inhibiting protein translation. (责任编辑：Doctor001) |
