Diverse roles of HP1 proteins in heterochromatin assembly and functions in fission yeast
Diverse roles of HP1 proteins in heterochromatin assembly and functions in fission yeast
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DOI：
10.1073/pnas.0813063106
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发表时间：
2009-06-02
影响因子：
11.1
通讯作者：
Grewal, Shiv I. S.
中科院分区：
文献类型：
--
作者：
Fischer, Tamas;Cui, Bowen;Grewal, Shiv I. S.
保守的染色体HP 1蛋白能够结合组蛋白H3在赖氨酸9甲基化，被认为提供了一个动态的平台，招募和/或扩散的各种调控蛋白参与不同的染色体过程。裂殖酵母裂殖酵母HP 1家族成员Chp 2和Swi 6对异染色质组装和转录沉默很重要，但它们的确切作用还不完全清楚。在这里，我们表明，Swi 6和Chp 2与组蛋白脱乙酰基酶（HDAC）蛋白复合物含有I类HDAC Clr 6和II类HDAC Clr 3（Snf 2/HDAC阻遏复合物的一个组成部分），这是关键的转录沉默的着丝粒重复的异染色质机制为目标。RNA聚合酶（Pol）II分布在单和双突变体背景的映射显示，Swi 6和Chp 2蛋白及其相关的HDAC复合物具有重叠的功能，限制Pol II占用跨近着丝粒异染色质结构域。纯化的Swi 6级分还含有参与各种染色体过程如染色质重塑和DNA复制的因子。此外，Swi 6与Mis 4蛋白（一种对姐妹染色单体凝聚力至关重要的凝聚素加载因子）以及着丝粒特异性组蛋白H3变体CENP-A共纯化，CENP-A以异染色质依赖性方式掺入染色质中。这些分析表明，在其他功能，HP 1蛋白与染色质修饰因子，反过来合作组装抑制染色质，从而排除了潜在的DNA序列的转录机器的访问。
Conserved chromosomal HP1 proteins capable of binding to histone H3 methylated at lysine 9 are believed to provide a dynamic platform for the recruitment and/or spreading of various regulatory proteins involved in diverse chromosomal processes. The fission yeast Schizosaccharomyces pombe HP1 family members Chp2 and Swi6 are important for heterochromatin assembly and transcriptional silencing, but their precise roles are not fully understood. Here, we show that Swi6 and Chp2 associate with histone deacetylase ( HDAC) protein complexes containing class I HDAC Clr6 and class II HDAC Clr3 ( a component of Snf2/HDAC repressor complex), which are critical for transcriptional silencing of centromeric repeats targeted by the heterochromatin machinery. Mapping of RNA polymerase (Pol) II distribution in single and double mutant backgrounds revealed that Swi6 and Chp2 proteins and their associated HDAC complexes have overlapping functions in limiting Pol II occupancy across pericentromeric heterochromatin domains. The purified Swi6 fraction also contains factors involved in various chromosomal processes such as chromatin remodeling and DNA replication. Also, Swi6 copurifies with Mis4 protein, a cohesin loading factor essential for sister chromatid cohesion, and with centromere-specific histone H3 variant CENP-A, which is incorporated into chromatin in a heterochromatin-dependent manner. These analyses suggest that among other functions, HP1 proteins associate with chromatin-modifying factors that in turn cooperate to assemble repressive chromatin; thus, precluding accessibility of underlying DNA sequences to transcriptional machinery.