A nucleosome contains two copies of each histone H2A, H2B, H3 and H4. Histone H3 K4me0 and K36me3 are two key chromatin marks for de novo DNA methylation catalyzed by DNA methyltransferases in mammals. However, it remains unclear whether K4me0 and K36me3 marks on both sister histone H3s regulate de novo DNA methylation independently or cooperatively. Here, taking advantage of the bivalent histone H3 system in yeast, we examined the contributions of K4 and K36 on sister histone H3s to genomic DNA methylation catalyzed by ectopically co-expressed murine Dnmt3a and Dnmt3L. The results show that lack of both K4me0 and K36me3 on one sister H3 tail, or lack of K4me0 and K36me3 on respective sister H3s results in a dramatic reduction of 5mC, revealing a synergy of two sister H3s in DNA methylation regulation. Accordingly, the Dnmt3a or Dnmt3L mutation that disrupts the interaction of ^Dnmt3aADD domain-H3K4me0, ^Dnmt3LADD domain-H3K4me0, or ^Dnmt3aPWWP domain-H3K36me3 causes a significant reduction of DNA methylation. These results support the model that each heterodimeric Dnmt3a-Dnmt3L reads both K4me0 and K36me3 marks on one tail of sister H3s, and the dimer of heterodimeric Dnmt3a-Dnmt3L recognizes two tails of sister histone H3s to efficiently execute de novo DNA methylation.

核小体包含两个组蛋白H2A，H2B，H3和H4的两个副本。组蛋白H3 K4me0和K36me3是哺乳动物DNA甲基转移酶催化的从头DNA甲基化的两个关键染色质标记。然而，尚不清楚两个姐妹组蛋白H3上的K4me0和K36me3标记是否重新调节DNA甲基化独立或协同进行。在这里，我们利用酵母中的二价组蛋白H3系统，研究了姐妹组蛋白H3上K4和K36对异位共表达鼠Dnmt3a和Dnmt3L催化的基因组DNA甲基化的贡献。结果表明，一个姊妹H3尾巴上既不存在K4me0和K36me3，又在各自姊妹H3上都不存在K4me0和K36me3，导致5mC急剧降低，揭示了两个姊妹H3在DNA甲基化调节中的协同作用。因此，Dnmt3a或Dnmt3L突变破坏了^Dnmt3a ADD域-H3K4me0，^Dnmt3L ADD域-H3K4me0或^Dnmt3a的相互作用PWWP域-H3K36me3导致DNA甲基化的显着减少。这些结果支持以下模型：每个异二聚体Dnmt3a-Dnmt3L都在姐妹H3的一条尾巴上同时读取K4me0和K36me3标记，异二聚体Dnmt3a-Dnmt3L的二聚体识别姐妹组蛋白H3s的两条尾巴，从而有效地进行了从头DNA甲基化。