Tethering RITS to a nascent transcript initiates RNAi- and heterochromatin-dependent gene silencing
Tethering RITS to a nascent transcript initiates RNAi- and heterochromatin-dependent gene silencing
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DOI：
10.1016/j.cell.2006.04.025
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发表时间：
2006-06-02
期刊：
影响因子：
64.5
通讯作者：
Moazed, Danesh
中科院分区：
文献类型：
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作者：
Buhler, Marc;Verdel, André;Moazed, Danesh
在裂殖酵母裂殖酵母中，RNA诱导的转录沉默（RITS）复合物已经被提出通过siRNA依赖的碱基配对相互作用靶向染色体以启动异染色质形成。在这里，我们发现RITS亚基Tas 3与正常活性的ura 4（+）基因的RNA转录本的连接沉默了ura 4（+）的表达。这种沉默依赖于功能性RNAi途径，需要异染色质蛋白Swi 6/HP 1、CIr 4/Suv 39 h和Sir 2，并伴随着ura 4（+）siRNA、组蛋白H3-赖氨酸9甲基化和Swi 6结合的产生。此外，新产生的ura 4（+）siRNA沉默第二个ura 4（+）等位基因的能力被保守的siRNA核酸酶Eri 1强烈抑制。令人惊讶的是，系留的ura 4（+）或插入着丝粒异染色质内的ura 4（+）或一些内源性着丝粒重复启动子的沉默与RNA聚合酶II占有率的变化无关。这些研究结果支持了一个模型，在该模型中，通过RITS介导的染色质修饰的新生转录物的目标，并表明，共转录加工事件在沉默机制中发挥主要作用。
In the fission yeast Schizosaccharomyces pombe, the RNA-Induced Transcriptional Silencing (RITS) complex has been proposed to target the chromosome via siRNA-dependent base-pairing interactions to initiate heterochromatin formation. Here we show that tethering of the RITS subunit, Tas3, to the RNA transcript of the normally active ura4(+) gene silences ura4(+) expression. This silencing depends on a functional RNAi pathway, requires the heterochromatin proteins, Swi6/HP1, CIr4/Suv39h, and Sir2, and is accompanied by the generation of ura4(+) siRNAs, histone H3-lysine 9 methylation, and Swi6 binding. Furthermore, the ability of the newly generated ura4(+) siRNAs; to silence a second ura4(+) allele in trans is strongly inhibited by the conserved siRNA nuclease, Eri1. Surprisingly, silencing of tethered ura4(+), or ura4(+) inserted within centromeric heterochromatin, or some of the endogenous centromeric repeat promoters, is not associated with changes in RNA polymerase II occupancy. These findings support a model in which targeting of nascent transcripts by RITS mediates chromatin modifications and suggest that cotranscriptional processing events play a primary role in the silencing mechanism.