Division of Developmental Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Building 6A Room 2A02, 6 Center Drive, Bethesda, MD, 20892, USA.
Sci Rep. 2021 Feb 18;11(1):4195. doi: 10.1038/s41598-021-82842-9.
Isw1 and Chd1 are ATP-dependent nucleosome-spacing enzymes required to establish regular arrays of phased nucleosomes near transcription start sites of yeast genes. Cells lacking both Isw1 and Chd1 have extremely disrupted chromatin, with weak phasing, irregular spacing and a propensity to form close-packed dinucleosomes. The Isw1 ATPase subunit occurs in two different remodeling complexes: ISW1a (composed of Isw1 and Ioc3) and ISW1b (composed of Isw1, Ioc2 and Ioc4). The Ioc4 subunit of ISW1b binds preferentially to the H3-K36me3 mark. Here we show that ISW1b is primarily responsible for setting nucleosome spacing and resolving close-packed dinucleosomes, whereas ISW1a plays only a minor role. ISW1b and Chd1 make additive contributions to dinucleosome resolution, such that neither enzyme is capable of resolving all dinucleosomes on its own. Loss of the Set2 H3-K36 methyltransferase partly phenocopies loss of Ioc4, resulting in increased dinucleosome levels with only a weak effect on nucleosome spacing, suggesting that Set2-mediated H3-K36 trimethylation contributes to ISW1b-mediated dinucleosome separation. The H4 tail domain is required for normal nucleosome spacing but not for dinucleosome resolution. We conclude that the nucleosome spacing and dinucleosome resolving activities of ISW1b and Chd1 are critical for normal global chromatin organisation.
Isw1 和 Chd1 是依赖于 ATP 的核小体间隔酶，对于在酵母基因的转录起始位点附近建立相定位的核小体阵列是必需的。同时缺乏 Isw1 和 Chd1 的细胞的染色质极度紊乱，具有较弱的相位、不规则的间隔和形成紧密包装二聚体的倾向。Isw1 ATP 酶亚基存在于两种不同的重塑复合物中：ISW1a（由 Isw1 和 Ioc3 组成）和 ISW1b（由 Isw1、Ioc2 和 Ioc4 组成）。ISW1b 中的 Ioc4 亚基优先结合 H3-K36me3 标记。在这里，我们表明 ISW1b 主要负责设定核小体间隔并解决紧密包装的二聚体，而 ISW1a 只起次要作用。ISW1b 和 Chd1 对二聚体的分辨率有累加作用，因此这两种酶都不能单独解决所有的二聚体。丧失 Set2 H3-K36 甲基转移酶的部分表型类似于 Ioc4 的丧失，导致二聚体水平增加，而核小体间隔仅受弱影响，这表明 Set2 介导的 H3-K36 三甲基化有助于 ISW1b 介导的二聚体分离。H4 尾巴结构域对于正常核小体间隔是必需的，但对于二聚体分辨率则不是必需的。我们得出结论，ISW1b 和 Chd1 的核小体间隔和二聚体分离活性对于正常的全局染色质组织至关重要。
