Polycomb repressive complex 2 (PRC2) is a histone methyltransferase that methylates histone H3 at Lysine 27. PRC2 is critical for epigenetic gene silencing, cellular differentiation and the formation of facultative heterochromatin. It can also promote or inhibit oncogenesis. Despite this importance, the molecular mechanisms by which PRC2 compacts chromatin are relatively understudied. Here, we visualized the binding of PRC2 to naked DNA in liquid at the single-molecule level using atomic force microscopy. Analysis of the resulting images showed PRC2, consisting of five subunits (EZH2, EED, SUZ12, AEBP2 and RBBP4), bound to a 2.5-kb DNA with an apparent dissociation constant ($K_{\rm{D}}^{{\rm{app}}}$) of 150 ± 12 nM. PRC2 did not show sequence-specific binding to a region of high GC content (76%) derived from a CpG island embedded in such a long DNA substrate. At higher concentrations, PRC2 compacted DNA by forming DNA loops typically anchored by two or more PRC2 molecules. Additionally, PRC2 binding led to a 3-fold increase in the local bending of DNA's helical backbone without evidence of DNA wrapping around the protein. We suggest that the bending and looping of DNA by PRC2, independent of PRC2's methylation activity, may contribute to heterochromatin formation and therefore epigenetic gene silencing.

中文翻译：

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通过液体中的AFM成像揭示了Polycomb阻抑复合物2弯曲和环化长DNA。

聚梳抑制复合物2（PRC2）是一种组蛋白甲基转移酶，可将赖氨酸27处的组蛋白H3甲基化。PRC2对于表观遗传基因沉默，细胞分化和兼性异染色质的形成至关重要。它也可以促进或抑制肿瘤发生。尽管有这种重要性，但PRC2压实染色质的分子机制还是相对不足的。在这里，我们使用原子力显微镜在单个分子水平上可视化了PRC2与液体中裸露的DNA的结合。对所得图像的分析显示，PRC2由五个亚基（EZH2，EED，SUZ12，AEBP2和RBBP4）组成，结合到具有表观解离常数（$ K _ {\ rm {D}} ^ {{\ rm {app}}} $）150±12 nM。PRC2没有显示出与嵌入在如此长的DNA底物中的CpG岛衍生的高GC含量区域（76％）的序列特异性结合。在较高浓度下，PRC2通过形成通常由两个或多个PRC2分子锚定的DNA环来压实DNA。此外，PRC2结合导致DNA螺旋骨架的局部弯曲增加了3倍，而没有DNA包裹在蛋白质周围的迹象。我们建议，PRC2对DNA的弯曲和环状作用不依赖于PRC2的甲基化活性，可能有助于异染色质的形成，并因此导致表观遗传基因沉默。螺旋状主链，无蛋白质包裹蛋白质的证据。我们建议，PRC2对DNA的弯曲和环状作用不依赖于PRC2的甲基化活性，可能有助于异染色质的形成，并因此导致表观遗传基因沉默。螺旋状主链，无蛋白质包裹蛋白质的证据。我们建议，PRC2对DNA的弯曲和环状作用不依赖于PRC2的甲基化活性，可能有助于异染色质的形成，并因此导致表观遗传基因沉默。