The Drosophila RNA methyltransferase, DmHen1, modifies germline piRNAs and single-stranded siRNAs in RISC
The Drosophila RNA methyltransferase, DmHen1, modifies germline piRNAs and single-stranded siRNAs in RISC
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DOI：
10.1016/j.cub.2007.06.030
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发表时间：
2007-07-17
期刊：
影响因子：
9.2
通讯作者：
Zamore, Phillip D.
中科院分区：
文献类型：
--
作者：
Horwich, Michael D.;Li, Chengjian;Zamore, Phillip D.
小分子沉默RNA通过一系列相关机制抑制基因表达，统称为RNA沉默途径[1，2]。在RNA干扰（RNAi）途径中[3]，小干扰mRNA（siRNA）保护细胞免受外来核酸（如病毒产生的核酸）的侵袭。相比之下，microRNAs（miRNAs）塑造内源性mRNA表达[4]。第三类小RNA，Piwi相互作用RNA（piRNA），保护基因组免受转座子的侵害[59]。在这里，我们报道了果蝇piRNA在其3'末端含有2'-O-甲基;这是先前报道的植物miRNA和siRNA [10]以及小鼠和大鼠piRNA [11，12，13]的修饰。植物小RNA甲基化由蛋白质HEN 1催化[10，14，15]。我们发现，DmHen 1，果蝇同源的HEN 1，甲基化的siRNA和piRNA的末端。在没有DmHenl的情况下，piRNA的长度和丰度降低，并且皮尔纳功能受到干扰。与植物HEN 1不同，DmHen 1作用于单链，而不是双链体，这解释了它如何可以使用siRNA（来自双链寡核苷酸）和piRNA（不来自双链寡核苷酸）作为底物[8，13]。siRNA的2 '-O-甲基化可能是RNAi-酶复合物RISC组装的最后一步，发生在Argonaute结合的siRNA双链体转化为单链RNA之后。
Small silencing RNAs repress gene expression by a set of related mechanisms collectively called RNA-silencing pathways [1, 2]. In the RNA interference (RNAi) pathway [3], small interfering mRNA (siRNAs) defend cells from invasion by foreign nucleic acids, such as those produced by viruses. In contrast, microRNAs (miRNAs) sculpt endogenous mRNA expression [4]. A third class of small RNAs, Piwi-interacting RNAs (piRNAs), defends the genome from transposons [59]. Here, we report that Drosophila piRNAs contain a 2'-O-methyl group on their 3' termini; this is a modification previously reported for plant miRNAs and siRNAs [10] and mouse and rat piRNAs [11,12,13]. Plant small-RNA methylation is catalyzed by the protein HEN1 [10, 14,15]. We find that DmHen1, the Drosophila homolog of HEN1, methylates the termini of siRNAs and piRNAs. Without DmHen1, the length and abundance of piRNAs are decreased, and piRNA function is perturbed. Unlike plant HEN1, DmHen1 acts on single strands, not duplexes, explaining how it can use as substrates both siRNAs-which derive from double-stranded precursors-and piRNAs-which do not [8,13]. 2'-O-methylation of siRNAs may be the final step in assembly of the RNAi-enzyme complex, RISC, occurring after an Argonaute-bound siRNA duplex is converted to single-stranded RNA.