Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD, USA.
PLoS Genet. 2013 Jun;9(6):e1003542. doi: 10.1371/journal.pgen.1003542. Epub 2013 Jun 6.
Mammalian DNA replication starts at distinct chromosomal sites in a tissue-specific pattern coordinated with transcription, but previous studies have not yet identified a chromatin modification that correlates with the initiation of DNA replication at particular genomic locations. Here we report that a distinct fraction of replication initiation sites in the human genome are associated with a high frequency of dimethylation of histone H3 lysine K79 (H3K79Me2). H3K79Me2-containing chromatin exhibited the highest genome-wide enrichment for replication initiation events observed for any chromatin modification examined thus far (23.39% of H3K79Me2 peaks were detected in regions adjacent to replication initiation events). The association of H3K79Me2 with replication initiation sites was independent and not synergistic with other chromatin modifications. H3K79 dimethylation exhibited wider distribution on chromatin during S-phase, but only regions with H3K79 methylation in G1 and G2 were enriched in replication initiation events. H3K79 was dimethylated in a region containing a functional replicator (a DNA sequence capable of initiating DNA replication), but the methylation was not evident in a mutant replicator that could not initiate replication. Depletion of DOT1L, the sole enzyme responsible for H3K79 methylation, triggered limited genomic over-replication although most cells could continue to proliferate and replicate DNA in the absence of methylated H3K79. Thus, prevention of H3K79 methylation might affect regulatory processes that modulate the order and timing of DNA replication. These data are consistent with the hypothesis that dimethylated H3K79 associates with some replication origins and marks replicated chromatin during S-phase to prevent re-replication and preserve genomic stability.
哺乳动物的 DNA 复制从组织特异性的不同染色体位点开始，与转录协调，但以前的研究尚未确定与特定基因组位置的 DNA 复制起始相关的染色质修饰。在这里，我们报告人类基因组中特定的复制起始位点与组蛋白 H3 赖氨酸 K79 的二甲基化（H3K79Me2）的高频相关。含有 H3K79Me2 的染色质在迄今为止检查的任何染色质修饰中显示出最高的全基因组复制起始事件富集（在复制起始事件附近的区域中检测到 23.39%的 H3K79Me2 峰）。H3K79Me2 与复制起始位点的关联是独立的，并且与其他染色质修饰没有协同作用。H3K79 在 S 期的染色质上表现出更广泛的分布，但只有在 G1 和 G2 中具有 H3K79 甲基化的区域在复制起始事件中富集。H3K79 在含有功能复制子（能够起始 DNA 复制的 DNA 序列）的区域中被二甲基化，但在不能起始复制的突变型复制子中没有明显的甲基化。DOT1L 的耗竭，唯一负责 H3K79 甲基化的酶，引发了有限的基因组过度复制，尽管大多数细胞可以在没有甲基化 H3K79 的情况下继续增殖和复制 DNA。因此，防止 H3K79 甲基化可能会影响调节 DNA 复制顺序和时间的调控过程。这些数据与以下假设一致，即二甲基化的 H3K79 与一些复制原点相关，并在 S 期标记复制的染色质，以防止重复制并维持基因组稳定性。
