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

项目摘要 异染色质由真核生物紧密致密的重复区域组成 染色体。它通过有丝分裂遗传，并在转录沉默中发挥作用， 着丝粒规范和基因组完整性，深刻影响表观遗传学 健康和疾病的机制。我们发现，人类的表观遗传 裂解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。 S.pombe着丝粒重复序列具有交替排列的小RNA簇 以及造成转录和复制冲突的复制起源 机械几乎是不可避免的。我们发现RNAi促进了RNA聚合酶的释放 (POL II)在S阶段，允许由领先链完成DNA复制 DNA聚合酶，招募组蛋白修饰Rik1复合体传播 异染色质与DNA复制。在没有RNAi的情况下，停滞的叉子 在没有组蛋白修饰的情况下通过同源重组(HR)修复，使HR 在没有RNAi的情况下是必不可少的，并减少了rDNA重复的拷贝数。这 模型可以解释非编码RNA和DNA修复中的许多参与 表观遗传沉默的例子，例如印记和X-失活。 最近，我们发现RNAi对静止细胞(G0)的生存是必不可少的，这是 在酵母中占主导地位，并在癌症、干细胞和神经元中发挥关键作用 疾病。基因筛查显示Rik1复合体和PolII都是 参与RNAi的这一新功能，涉及异染色质沉默和 DNA修复。S.pombe是细胞周期研究的优秀模型系统， 异染色质沉默和RNAi。我们将研究DNA复制的作用， 异染色组蛋白中RNA聚合酶的释放、DNA重组和修复 Rik1复合体和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.