Chromatin-based epigenetic memory relies on the accurate distribution of parental histone H3–H4 tetramers to newly replicated DNA strands. Mcm2, a subunit of the replicative helicase, and Dpb3/4, subunits of DNA polymerase ε, govern parental histone H3–H4 deposition to the lagging and leading strands, respectively. However, their contribution to epigenetic inheritance remains controversial. Here, using fission yeast heterochromatin inheritance systems that eliminate interference from initiation pathways, we show that a Mcm2 histone binding mutation severely disrupts heterochromatin inheritance, while mutations in Dpb3/4 cause only moderate defects. Surprisingly, simultaneous mutations of Mcm2 and Dpb3/4 stabilize heterochromatin inheritance. eSPAN (enrichment and sequencing of protein-associated nascent DNA) analyses confirmed the conservation of Mcm2 and Dpb3/4 functions in parental histone H3–H4 segregation, with their combined absence showing a more symmetric distribution of parental histone H3–H4 than either single mutation alone. Furthermore, the FACT histone chaperone regulates parental histone transfer to both strands and collaborates with Mcm2 and Dpb3/4 to maintain parental histone H3–H4 density and faithful heterochromatin inheritance. These results underscore the importance of both symmetric distribution of parental histones and their density at daughter strands for epigenetic inheritance and unveil distinctive properties of parental histone chaperones during DNA replication.

中文翻译：

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亲代组蛋白分离和表观遗传中组蛋白伴侣的协调

基于染色质的表观遗传记忆依赖于亲本组蛋白 H3-H4 四聚体到新复制的 DNA 链的准确分布。 Mcm2（复制解旋酶的亚基）和 Dpb3/4（DNA 聚合酶 ε 的亚基）分别控制亲本组蛋白 H3-H4 沉积到滞后链和前导链。然而，它们对表观遗传的贡献仍然存在争议。在这里，使用消除起始途径干扰的裂殖酵母异染色质遗传系统，我们发现 Mcm2 组蛋白结合突变严重破坏异染色质遗传，而 Dpb3/4 的突变仅导致中度缺陷。令人惊讶的是，Mcm2 和 Dpb3/4 的同时突变稳定了异染色质遗传。 eSPAN（蛋白质相关新生 DNA 富集和测序）分析证实了 Mcm2 和 Dpb3/4 在亲代组蛋白 H3-H4 分离中功能的保守性，它们的组合缺失表明亲代组蛋白 H3-H4 的分布比任一单一突变更加对称独自的。此外，FACT 组蛋白伴侣调节亲本组蛋白向两条链的转移，并与 Mcm2 和 Dpb3/4 合作维持亲本组蛋白 H3-H4 密度和忠实的异染色质遗传。这些结果强调了亲本组蛋白的对称分布及其在子链上的密度对于表观遗传的重要性，并揭示了亲本组蛋白伴侣在 DNA 复制过程中的独特特性。