One of the most extensive forms of natural genome editing occurs in ciliates, a group of microbial eukaryotes. Ciliate germline and somatic genomes are contained in distinct nuclei within the same cell. During the massive reorganization process of somatic genome development, ciliates eliminate tens of thousands of DNA sequences from a germline genome copy. Recently, we showed that the chromatin remodeler ISWI1 is required for somatic genome development in the ciliate Paramecium tetraurelia. Here, we describe two high similarity paralogous proteins, ICOPa and ICOPb, essential for their genome editing. ICOPa and ICOPb are highly divergent from known proteins; the only domain detected showed distant homology to the WSD (WHIM2+WHIM3) motif. We show that both ICOPa and ICOPb interact with the chromatin remodeler ISWI1. Upon ICOP knockdown, changes in alternative DNA excision boundaries and nucleosome densities are similar to those observed for ISWI1 knockdown. We thus propose that a complex comprising ISWI1 and either or both ICOPa and ICOPb are needed for Paramecium's precise genome editing.

中文翻译：

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ISWI1 复合蛋白促进草履虫发育基因组编辑


最广泛的自然基因组编辑形式之一发生在纤毛虫中，纤毛虫是一组微生物真核生物。纤毛生殖系和体细胞基因组包含在同一细胞内的不同细胞核中。在体细胞基因组发育的大规模重组过程中，纤毛虫从种系基因组拷贝中消除了数以万计的 DNA 序列。最近，我们表明染色质重塑基因 ISWI1 是纤毛虫 Paramecium tetraurelia 体细胞基因组发育所必需的。在这里，我们描述了两种高度相似的旁系同源蛋白 ICOPa 和 ICOPb，它们对它们的基因组编辑至关重要。ICOPa 和 ICOPb 与已知蛋白质高度不同;唯一检测到的结构域与 WSD （WHIM2+WHIM3） 基序具有远距离同源性。我们表明 ICOPa 和 ICOPb 都与染色质重塑剂 ISWI1 相互作用。ICOP 敲低后，选择性 DNA 切除边界和核小体密度的变化与 ISWI1 敲低时观察到的变化相似。因此，我们提出草履虫的精确基因组编辑需要一种包含 ISWI1 和 ICOPa 和 ICOPb 的复合物。