Iida Tetsushi, Araki Hiroyuki
Division of Microbial Genetics, National Institute of Genetics, SOKENDAI, Mishima, Shizuoka 411-8540, Japan.
Mol Cell Biol. 2004 Jan;24(1):217-27. doi: 10.1128/MCB.24.1.217-227.2004.
Relocation of euchromatic genes near the heterochromatin region often results in mosaic gene silencing. In Saccharomyces cerevisiae, cells with the genes inserted at telomeric heterochromatin-like regions show a phenotypic variegation known as the telomere-position effect, and the epigenetic states are stably passed on to following generations. Here we show that the epigenetic states of the telomere gene are not stably inherited in cells either bearing a mutation in a catalytic subunit (Pol2) of replicative DNA polymerase epsilon (Pol epsilon) or lacking one of the nonessential and histone fold motif-containing subunits of Pol epsilon, Dpb3 and Dpb4. We also report a novel and putative chromatin-remodeling complex, ISW2/yCHRAC, that contains Isw2, Itc1, Dpb3-like subunit (Dls1), and Dpb4. Using the single-cell method developed in this study, we demonstrate that without Pol epsilon and ISW2/yCHRAC, the epigenetic states of the telomere are frequently switched. Furthermore, we reveal that Pol epsilon and ISW2/yCHRAC function independently: Pol epsilon operates for the stable inheritance of a silent state, while ISW2/yCHRAC works for that of an expressed state. We therefore propose that inheritance of specific epigenetic states of a telomere requires at least two counteracting regulators.
常染色质基因重定位到异染色质区域附近通常会导致嵌合基因沉默。在酿酒酵母中，基因插入端粒异染色质样区域的细胞表现出一种称为端粒位置效应的表型变异，并且这种表观遗传状态会稳定地传递给后代。在这里，我们表明，在复制性DNA聚合酶ε（Pol ε）的催化亚基（Pol2）发生突变的细胞中，或者在缺乏Pol ε的非必需且含组蛋白折叠基序的亚基之一Dpb3和Dpb4的细胞中，端粒基因的表观遗传状态不会稳定遗传。我们还报告了一种新型的假定染色质重塑复合体ISW2/yCHRAC，它包含Isw2、Itc1、Dpb3样亚基（Dls1）和Dpb4。使用本研究中开发的单细胞方法，我们证明，没有Pol ε和ISW2/yCHRAC，端粒的表观遗传状态会频繁切换。此外，我们揭示Pol ε和ISW2/yCHRAC独立发挥作用：Pol ε负责沉默状态的稳定遗传，而ISW2/yCHRAC负责表达状态的稳定遗传。因此，我们提出端粒特定表观遗传状态的遗传至少需要两种相互拮抗的调节因子。
