Nucleosomes composed of histones are the fundamental units around which DNA is wrapped to form chromatin. Transcriptionally active euchromatin or repressive heterochromatin is regulated in part by the addition or removal of histone post-translational modifications (PTMs) by “writer” and “eraser” enzymes, respectively. Nucleosomal PTMs are recognized by a variety of “reader” proteins that alter gene expression accordingly. The histone tails of the evolutionarily divergent eukaryotic parasite Trypanosoma brucei have atypical sequences and PTMs distinct from those often considered universally conserved. Here we identify 65 predicted readers, writers, and erasers of histone acetylation and methylation encoded in the T. brucei genome and, by epitope tagging, systemically localize 60 of them in the parasite's bloodstream form. ChIP-seq shows that 15 candidate proteins associate with regions of RNAPII transcription initiation. Eight other proteins show a distinct distribution with specific peaks at a subset of RNAPII transcription termination regions marked by RNAPIII-transcribed tRNA and snRNA genes. Proteomic analyses identify distinct protein interaction networks comprising known chromatin regulators and novel trypanosome-specific components. Notably, several SET- and Bromo-domain protein networks suggest parallels to RNAPII promoter–associated complexes in conventional eukaryotes. Further, we identify likely components of TbSWR1 and TbNuA4 complexes whose enrichment coincides with the SWR1-C exchange substrate H2A.Z at RNAPII transcription start regions. The systematic approach used provides details of the composition and organization of the chromatin regulatory machinery in T. brucei and establishes a route to explore divergence from eukaryotic norms in an evolutionarily ancient but experimentally accessible eukaryote.

中文翻译：

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对布氏锥虫染色质因子的系统分析确定了与转录起始和终止位点相关的新型蛋白质相互作用网络


由组蛋白组成的核小体是 DNA 包裹形成染色质的基本单位。转录活性常染色质或抑制性异染色质部分通过“写入”酶和“擦除”酶分别添加或去除组蛋白翻译后修饰 (PTM) 来调节。核小体 PTM 被多种“阅读器”蛋白识别，从而相应地改变基因表达。进化上不同的真核寄生虫布氏锥虫的组蛋白尾部具有非典型序列和 PTM，与通常被认为普遍保守的序列和 PTM 不同。在这里，我们鉴定了布氏锥虫基因组中编码的 65 个预测的组蛋白乙酰化和甲基化读取器、写入器和擦除器，并通过表位标记，系统地将其中 60 个定位在寄生虫的血流形式中。 ChIP-seq 显示 15 种候选蛋白与 RNAPII 转录起始区域相关。其他八种蛋白质显示出独特的分布，在由 RNAPIII 转录的 tRNA 和 snRNA 基因标记的 RNAPII 转录终止区子集上有特定峰。蛋白质组学分析确定了不同的蛋白质相互作用网络，包括已知的染色质调节因子和新型锥虫特异性成分。值得注意的是，一些 SET 和 Bromo 结构域蛋白网络表明与传统真核生物中的 RNAPII 启动子相关复合物相似。此外，我们还鉴定了 TbSWR1 和 TbNuA4 复合物的可能成分，其富集与 RNAPII 转录起始区域的 SWR1-C 交换底物 H2A.Z 一致。所使用的系统方法提供了T.染色质调节机制的组成和组织的详细信息。 brucei 并建立了一条探索进化古老但可通过实验获得的真核生物与真核生物规范的分歧的路线。