Faculty of Life and Environmental Sciences, Initiative for the Promotion of Young Scientists' Independent Research, University of Tsukuba, Tsukuba, Japan.
PLoS One. 2011;6(12):e28980. doi: 10.1371/journal.pone.0028980. Epub 2011 Dec 21.
Histone modifications are important epigenetic features of chromatin that must be replicated faithfully. However, the molecular mechanisms required to duplicate and maintain histone modification patterns in chromatin remain to be determined. Here, we show that the introduction of histone modifications into newly deposited nucleosomes depends upon their location in the chromosome. In Saccharomyces cerevisiae, newly deposited nucleosomes consisting of newly synthesized histone H3-H4 tetramers are distributed throughout the entire chromosome. Methylation of lysine 4 on histone H3 (H3-K4), a hallmark of euchromatin, is introduced into these newly deposited nucleosomes, regardless of whether the neighboring preexisting nucleosomes harbor the K4 mutation in histone H3. Furthermore, if the heterochromatin-binding protein Sir3 is unavailable during DNA replication, histone H3-K4 methylation is introduced onto newly deposited nucleosomes in telomeric heterochromatin. Thus, a conservative distribution model most accurately explains the inheritance of histone modifications because the location of histones within euchromatin or heterochromatin determines which histone modifications are introduced.
组蛋白修饰是染色质中重要的表观遗传特征，必须忠实复制。然而，复制和维持染色质中组蛋白修饰模式所需的分子机制仍有待确定。在这里，我们表明，引入新沉积核小体中的组蛋白修饰取决于它们在染色体中的位置。在酿酒酵母中，由新合成的组蛋白 H3-H4 四聚体组成的新沉积核小体分布在整个染色体上。组蛋白 H3 赖氨酸 4 的甲基化（H3-K4）是常染色质的标志，被引入这些新沉积的核小体中，而不管相邻的预先存在的核小体是否携带组蛋白 H3 中的 K4 突变。此外，如果在 DNA 复制过程中没有异染色质结合蛋白 Sir3，则组蛋白 H3-K4 甲基化会被引入端粒异染色质中的新沉积核小体上。因此，保守的分配模型最能准确地解释组蛋白修饰的遗传，因为组蛋白在常染色质或异染色质中的位置决定了引入哪些组蛋白修饰。
