Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, NC 27599, USA.
Genetics. 2012 Oct;192(2):371-84. doi: 10.1534/genetics.112.142349. Epub 2012 Jul 30.
DNA replication is a highly regulated process that is initiated from replication origins, but the elements of chromatin structure that contribute to origin activity have not been fully elucidated. To identify histone post-translational modifications important for DNA replication, we initiated a genetic screen to identify interactions between genes encoding chromatin-modifying enzymes and those encoding proteins required for origin function in the budding yeast Saccharomyces cerevisiae. We found that enzymes required for histone H3K4 methylation, both the histone methyltransferase Set1 and the E3 ubiquitin ligase Bre1, are required for robust growth of several hypomorphic replication mutants, including cdc6-1. Consistent with a role for these enzymes in DNA replication, we found that both Set1 and Bre1 are required for efficient minichromosome maintenance. These phenotypes are recapitulated in yeast strains bearing mutations in the histone substrates (H3K4 and H2BK123). Set1 functions as part of the COMPASS complex to mono-, di-, and tri-methylate H3K4. By analyzing strains lacking specific COMPASS complex members or containing H2B mutations that differentially affect H3K4 methylation states, we determined that these replication defects were due to loss of H3K4 di-methylation. Furthermore, histone H3K4 di-methylation is enriched at chromosomal origins. These data suggest that H3K4 di-methylation is necessary and sufficient for normal origin function. We propose that histone H3K4 di-methylation functions in concert with other histone post-translational modifications to support robust genome duplication.
DNA 复制是一个高度调控的过程，它从复制起点开始，但对染色质结构元素有助于起源活性的因素尚未完全阐明。为了确定对 DNA 复制重要的组蛋白翻译后修饰，我们启动了一个遗传筛选，以鉴定编码染色质修饰酶的基因与编码芽殖酵母酿酒酵母中起源功能所需蛋白的基因之间的相互作用。我们发现，组蛋白 H3K4 甲基化所需的酶，包括组蛋白甲基转移酶 Set1 和 E3 泛素连接酶 Bre1，对于几个弱复制突变体（包括 cdc6-1）的强大生长都是必需的。这些酶在 DNA 复制中的作用一致，我们发现 Set1 和 Bre1 都需要有效的微染色体维持。这些表型在携带组蛋白底物（H3K4 和 H2BK123）突变的酵母菌株中得到了重现。Set1 作为 COMPASS 复合物的一部分，对 H3K4 进行单、二和三甲基化。通过分析缺乏特定 COMPASS 复合物成员或含有不同影响 H3K4 甲基化状态的 H2B 突变的菌株，我们确定这些复制缺陷是由于 H3K4 二甲基化的丧失。此外，组蛋白 H3K4 二甲基化在染色体起点处富集。这些数据表明，H3K4 二甲基化是正常起源功能所必需的和充分的。我们提出，组蛋白 H3K4 二甲基化与其他组蛋白翻译后修饰协同作用，支持稳健的基因组复制。
