DNA sequence templates adjacent nucleosome and ORC sites at gene amplification origins in Drosophila.
DNA sequence templates adjacent nucleosome and ORC sites at gene amplification origins in Drosophila.
复制标题
DOI：
10.1093/nar/gkv766
复制
发表时间：
2015-10-15
影响因子：
14.9
通讯作者：
Calvi BR
中科院分区：
文献类型：
--
作者：
Liu J;Zimmer K;Rusch DB;Paranjape N;Podicheti R;Tang H;Calvi BR
DNA复制的真核起点由起点识别复合物（ORC）结合，所述起点识别复合物支撑复制前复合物（pre-RC）的组装，所述复制前复合物随后被激活以启动复制。前RC组装和激活都受到表观基因组发育变化的强烈影响，但分子机制仍不完全确定。我们一直在研究果蝇中负责发育基因扩增的起源的激活。在卵子发生的特定时间，体细胞滤泡细胞从基因组复制转变为来自六个扩增子起点的基因座特异性复制。以前的证据表明，这些扩增子的起源是由核小体乙酰化激活，但这如何影响起源染色质是未知的。在这里，我们研究核小体的位置在卵泡细胞中使用微球菌核酸酶消化与Ilumina测序。结果表明，ORC结合位点和其他必需的起源序列是核小体缺失区（NDRs）。扩增子处的核小体位置在发育阶段之间高度相似，在发育阶段期间ORC结合或不结合，表明作为NDR不足以指定ORC结合。重要的是，这些数据表明，核小体和ORC对DNA序列和结构有相反的偏好。我们提出，核小体超乙酰化促进前RC组装到相邻的DNA序列，这是不利的核小体，但有利于ORC。
Eukaryotic origins of DNA replication are bound by the origin recognition complex (ORC), which scaffolds assembly of a pre-replicative complex (pre-RC) that is then activated to initiate replication. Both pre-RC assembly and activation are strongly influenced by developmental changes to the epigenome, but molecular mechanisms remain incompletely defined. We have been examining the activation of origins responsible for developmental gene amplification in Drosophila. At a specific time in oogenesis, somatic follicle cells transition from genomic replication to a locus-specific replication from six amplicon origins. Previous evidence indicated that these amplicon origins are activated by nucleosome acetylation, but how this affects origin chromatin is unknown. Here, we examine nucleosome position in follicle cells using micrococcal nuclease digestion with Ilumina sequencing. The results indicate that ORC binding sites and other essential origin sequences are nucleosome-depleted regions (NDRs). Nucleosome position at the amplicons was highly similar among developmental stages during which ORC is or is not bound, indicating that being an NDR is not sufficient to specify ORC binding. Importantly, the data suggest that nucleosomes and ORC have opposite preferences for DNA sequence and structure. We propose that nucleosome hyperacetylation promotes pre-RC assembly onto adjacent DNA sequences that are disfavored by nucleosomes but favored by ORC.