RNAi, Histone Modification and the DDB1/CPSF-like Complex Rik1

项目摘要 异染色质包含真核生物的紧密压缩的重复区域， 染色体它通过有丝分裂遗传，并在转录沉默中发挥作用， 着丝粒的特化和基因组的完整性，这深刻地影响了表观遗传 健康和疾病的机制。我们已经发现， 裂殖酵母中的异染色质需要RNA干扰（RNAi）来引导 组蛋白修饰，发生在细胞周期的DNA复制阶段。 粟酒裂殖酵母着丝粒重复序列具有小RNA簇的交替排列 和复制起点，使转录和复制的碰撞 机器几乎不可避免。我们发现RNAi促进了RNA聚合酶的释放， (Pol II）在S期，允许前导链完成DNA复制 DNA聚合酶，它招募组蛋白修饰Rik 1复合物进行扩散 异染色质沿着DNA复制。在没有RNAi的情况下， 通过同源重组（HR）修复而不进行组蛋白修饰，因此HR是 在没有RNAi的情况下是必需的，并且减少rDNA重复的拷贝数。这 一个模型可以解释非编码RNA和DNA修复在许多 表观遗传沉默的例子，如印记和X-失活。 最近，我们发现RNAi对于静止期细胞（G 0）的生存力是必需的， 在酵母中占主导地位，在癌症、干细胞和神经细胞中发挥关键作用。 疾病基因筛选显示，Rik 1复合体和Pol II都是 参与RNAi的这种新功能，涉及异染色质沉默和 DNA修复粟酒裂殖酵母是细胞周期研究的杰出模式系统， 异染色质沉默和RNAi。我们将研究DNA复制的作用， 异染色质组蛋白中的RNA聚合酶释放、DNA重组和修复 Rik 1复合物和RNAi介导的修饰。

Project Summary Heterochromatin comprises tightly compacted repetitive regions of eukaryotic chromosomes. It is inherited through mitosis and has roles in transcriptional silencing, centromere specification and genome integrity, which profoundly impact epigenetic mechanisms in health and disease. We have found that the epigenetic inheritance of heterochromatin in the fission yeast S.pombe requires RNA interference (RNAi) to guide histone modification, which occurs during the DNA replication phase of the cell cycle. S.pombe centromeric repeats have an alternating arrangement of small RNA clusters and origins of replication that makes collision of the transcription and replication machineries all but inevitable. We found that RNAi promotes release of RNA polymerase (Pol II) during S phase, allowing completion of DNA replication by the leading strand DNA polymerase, which recruits the histone-modifying Rik1 complex to spread heterochromatin along with DNA replication. In the absence of RNAi, stalled forks are repaired by homologous recombination (HR) without histone modification, so that HR is essential in the absence of RNAi, and reduces the copy number of rDNA repeats. This model may explain the participation of non-coding RNA and DNA repair in many examples of epigenetic silencing, such as imprinting and X-inactivation. Recently, we have found that RNAi is essential for viability in quiescent cells (G0), which are predominant in yeast and play critical roles in cancer, stem cells and neuronal disease. Genetic screens have revealed that the Rik1 complex and Pol II are both involved in this novel function for RNAi, implicating both heterochromatic silencing and DNA repair. S.pombe is an outstanding model system for cell cycle research, heterochromatic silencing, and RNAi. We will examine the roles of DNA replication, RNA Polymerase release, DNA recombination and repair in heterochromatic histone modification mediated by the Rik1 complex and RNAi.