A composite DNA element that functions as a maintainer required for epigenetic inheritance of heterochromatin

Epigenetic inheritance of heterochromatin requires sequence - independent propagation mechanisms and input from DNA sequence, but how DNA contributes to inheritance is not understood. Here, we identify a DNA element ( term ed the “maintainer” ) that is necessary and sufficient for epigenetic inheritance of preexisting histone H3 lysine 9 methylation (H3K9me) and heterochromatin i n the fission yeast Schizosaccharomyces pombe . In wild - type cells, d espite its requirement for maintenance of H3K9me, the maintainer cannot establish de novo gene silencing. The maintainer is a composite 1307 - base pair DNA element with binding sites for the Atf1/Pcr1 and Deb1 transcription factors and the O rigin R ecognition C omplex (ORC) and can be converted to a silencer in cells with lower rates of H3K9me turnover , suggesting that it participate s in recruiting the H3K9 methyltransferase Clr4 / Suv39h . T hese results suggest tha t histone H3K9me is only heritable when it can collaborate with maintainer - associated DNA - binding proteins that help recruit the enzyme responsible for its epigenetic deposition . Examination of genomic localization of Atf1/Pcr1, Deb1 and ORC in S.pombe

异染色质（heterochromatin）的表观遗传继承（epigenetic inheritance）需要不依赖序列的传播机制以及DNA序列的参与，但DNA如何参与这一遗传过程目前仍未阐明。本研究在粟酒裂殖酵母（Schizosaccharomyces pombe，简称S.pombe）中鉴定出一种被称为“维持元件（maintainer）”的DNA元件，其对于已存在的组蛋白H3赖氨酸9甲基化（histone H3 lysine 9 methylation, H3K9me）和异染色质的表观遗传继承既是必需的，也是充分的。在野生型细胞中，尽管该维持元件对于维持H3K9me是必需的，但它无法介导从头基因沉默。该维持元件是一段长1307碱基对的复合DNA元件，带有Atf1/Pcr1、Deb1转录因子（transcription factors）以及起始识别复合物（Origin Recognition Complex, ORC）的结合位点；在H3K9me周转速率较低的细胞中，它可被转化为沉默子（silencer），这提示其参与招募H3K9甲基转移酶Clr4/Suv39h。上述结果表明，组蛋白H3K9me仅在能够与维持元件相关的DNA结合蛋白协同作用时才可遗传——这类结合蛋白可帮助招募负责其表观遗传沉积的酶。本研究对粟酒裂殖酵母中Atf1/Pcr1、Deb1以及ORC的基因组定位展开了分析。