Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.
Graduate School of Chemical Science and Engineering, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.
Cell Rep. 2021 Aug 17;36(7):109540. doi: 10.1016/j.celrep.2021.109540.
FACT (facilitate chromatin transcription) is involved in heterochromatic silencing, but its mechanisms and function remain unclear. We reveal that the Spt16 recruitment mechanism operates in two distinct ways in heterochromatin. First, Pob3 mediates Spt16 recruitment onto the heterochromatin through its Spt16 dimerization and tandem PH domains. Without Pob3, Spt16 recruitment is partially reduced, exhibiting a silencing defect and impaired H2A/H2B organization. Second, heterochromatin protein 1 (HP1)/Swi6 mediates Spt16 recruitment onto the heterochromatin by physical interaction of the Swi6 chromo-shadow domain (CSD) and Spt16 peptidase-like domains. Several CSD mutants are tested for Spt16 binding activity, and the charged loop connecting β1 and β2 is critical for Spt16 binding and heterochromatic silencing. Loss of these pathways causes a severe defect in H3K9 methylation and HP1/Swi6 localization in the pericentromeric region, exhibiting transcriptional silencing defects and disordered heterochromatin. Our findings suggest that FACT and HP1/Swi6 work intimately to regulate heterochromatin organization.
FACT（促进染色质转录）参与异染色质沉默，但它的机制和功能仍不清楚。我们揭示了 Spt16 的募集机制在异染色质中以两种不同的方式运作。首先，Pob3 通过其 Spt16 二聚化和串联 PH 结构域介导 Spt16 募集到异染色质上。没有 Pob3，Spt16 的募集会部分减少，表现出沉默缺陷和 H2A/H2B 组织受损。其次，异染色质蛋白 1（HP1）/Swi6 通过 Swi6 染色质阴影域（CSD）和 Spt16 肽酶样结构域的物理相互作用介导 Spt16 募集到异染色质上。测试了几种 CSD 突变体的 Spt16 结合活性，连接β1 和β2 的带电环对于 Spt16 结合和异染色质沉默至关重要。这些途径的缺失会导致组蛋白 H3K9 甲基化和 HP1/Swi6 在着丝粒周围区域的定位严重缺陷，表现出转录沉默缺陷和异染色质紊乱。我们的发现表明，FACT 和 HP1/Swi6 密切合作调节异染色质的组织。
