Swd2/Cps35 determines H3K4 tri-methylation via interactions with Set1 and Rad6_Chromatin occupancy of Set1 in several strains

Histone H3K4 tri-methylation (H3K4me3) catalyzed by Set1/COMPASS, is a prominent epigenetic mark found in promoter-proximal regions of actively transcribed genes. H3K4me3 relies on prior monoubiquitination at the histone H2B (H2Bub) by Rad6 and Bre1. Swd2/Cps35, a Set1/COMPASS component, has been proposed as a key player in facilitating H2Bub-dependent H3K4me3. However, a more comprehensive investigation regarding the relationship among Rad6, Swd2 and Set1 is required to further understand the mechanisms and functions of the H3K4 methylation. We investigated the genome-wide occupancy patterns of Rad6, Swd2 and Set1 under various genetic conditions, aiming to clarify the roles of Set1 and Rad6 for occupancy of Swd2. Swd2 peaks appear on both 5’region and 3’region of genes, which are overlapped with its tightly bound two complexes, Set1 and CPF (Cleavage and Polyadenylation Factor), respectively. In the absence of Rad6/H2Bub, Set1 predominantly localized to the 5ʹ region of genes, while Swd2 lost all the chromatin binding. However, in the absence of Set1, Swd2 occupancy near the 5’region was impared and rather increased in the 3’ region. This study highlights that catalytic activity of Rad6 is essential for all the ways of Swd2’s binding to the transcribed genes and Set1 redistributes the Swd2 to 5’region for accomplishments of H3K4me3 in the genome-wide level.由Set1/COMPASS复合物催化的组蛋白H3K4三甲基化（H3K4me3），是活跃转录基因启动子近端区域中广泛存在的典型表观遗传标记。H3K4me3的形成依赖于Rad6与Bre1介导的组蛋白H2B单泛素化（H2Bub）。作为Set1/COMPASS复合物的组分之一，Swd2/Cps35被认为是介导依赖于H2Bub的H3K4me3修饰的关键因子。然而，目前仍需针对Rad6、Swd2与Set1三者间的相互关系开展更全面的研究，以进一步阐明H3K4甲基化的调控机制与生物学功能。 本研究在多种遗传条件下，检测了Rad6、Swd2与Set1的全基因组占据模式，旨在阐明Set1与Rad6对Swd2染色质占据的调控作用。Swd2的染色质结合峰同时分布于基因的5'端区域与3'端区域，分别与其紧密结合的两种复合物——Set1复合物与CPF（剪切与多聚腺苷酸化因子）——相重叠。 在Rad6/H2Bub缺失时，Set1主要定位于基因的5'端区域，而Swd2则完全丧失了染色质结合能力。但在Set1缺失的条件下，Swd2在基因5'端区域的染色质占据水平显著受损，反而在3'端区域出现占据水平升高。本研究证实，Rad6的催化活性是Swd2结合所有转录基因的必要条件，而Set1可将Swd2重新招募至基因5'端区域，从而在全基因组水平完成H3K4me3修饰。