Division of Gene Regulation, Netherlands Cancer Institute, Netherlands Proteomics Centre, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands.
Epigenetics Chromatin. 2011 Feb 3;4(1):2. doi: 10.1186/1756-8935-4-2.
Methylation of histone H3 lysine 79 (H3K79) by Dot1 is highly conserved among species and has been associated with both gene repression and activation. To eliminate indirect effects and examine the direct consequences of Dot1 binding and H3K79 methylation, we investigated the effects of targeting Dot1 to different positions in the yeast genome.
Targeting Dot1 did not activate transcription at a euchromatic locus. However, chromatin-bound Dot1 derepressed heterochromatin-mediated gene silencing over a considerable distance. Unexpectedly, Dot1-mediated derepression was established by both a H3K79 methylation-dependent and a methylation-independent mechanism; the latter required the histone acetyltransferase Gcn5. By monitoring the localization of a fluorescently tagged telomere in living cells, we found that the targeting of Dot1, but not its methylation activity, led to the release of a telomere from the repressive environment at the nuclear periphery. This probably contributes to the activity-independent derepression effect of Dot1.
Targeting of Dot1 promoted gene expression by antagonizing gene repression through both histone methylation and chromatin relocalization. Our findings show that binding of Dot1 to chromatin can positively affect local gene expression by chromatin rearrangements over a considerable distance.
组蛋白 H3 赖氨酸 79（H3K79）的 Dot1 甲基化在物种间高度保守，与基因抑制和激活都有关联。为了消除间接影响并研究 Dot1 结合和 H3K79 甲基化的直接后果，我们研究了将 Dot1 靶向酵母基因组中不同位置的效果。
Dot1 的靶向并没有在常染色质基因座上激活转录。然而，结合在染色质上的 Dot1 使异染色质介导的基因沉默在相当大的距离上失活。出乎意料的是，Dot1 介导的去抑制作用是通过 H3K79 甲基化依赖性和非甲基化依赖性机制建立的；后者需要组蛋白乙酰转移酶 Gcn5。通过监测活细胞中荧光标记的端粒的定位，我们发现 Dot1 的靶向，而不是其甲基化活性，导致端粒从核周的抑制环境中释放出来。这可能有助于 Dot1 的无活性去抑制效应。
Dot1 的靶向通过组蛋白甲基化和染色质重定位来拮抗基因抑制，从而促进基因表达。我们的研究结果表明，Dot1 与染色质的结合可以通过相当大的距离上的染色质重排来积极影响局部基因表达。
