BACKGROUND Chromatin organization is central to precise control of gene expression. In various eukaryotic species, domains of pervasive cis-chromatin interactions demarcate functional domains of the genomes. In nematode Caenorhabditis elegans, however, pervasive chromatin contact domains are limited to the dosage-compensated sex chromosome, leaving the principle of C. elegans chromatin organization unclear. Transcription factor III C (TFIIIC) is a basal transcription factor complex for RNA polymerase III, and is implicated in chromatin organization. TFIIIC binding without RNA polymerase III co-occupancy, referred to as extra-TFIIIC binding, has been implicated in insulating active and inactive chromatin domains in yeasts, flies, and mammalian cells. Whether extra-TFIIIC sites are present and contribute to chromatin organization in C. elegans remains unknown. RESULTS We identified 504 TFIIIC-bound sites absent of RNA polymerase III and TATA-binding protein co-occupancy characteristic of extra-TFIIIC sites in C. elegans embryos. Extra-TFIIIC sites constituted half of all identified TFIIIC binding sites in the genome. Extra-TFIIIC sites formed dense clusters in cis. The clusters of extra-TFIIIC sites were highly over-represented within the distal arm domains of the autosomes that presented a high level of heterochromatin-associated histone H3K9 trimethylation (H3K9me3). Furthermore, extra-TFIIIC clusters were embedded in the lamina-associated domains. Despite the heterochromatin environment of extra-TFIIIC sites, the individual clusters of extra-TFIIIC sites were devoid of and resided near the individual H3K9me3-marked regions. CONCLUSION Clusters of extra-TFIIIC sites were pervasive in the arm domains of C. elegans autosomes, near the outer boundaries of H3K9me3-marked regions. Given the reported activity of extra-TFIIIC sites in heterochromatin insulation in yeasts, our observation raised the possibility that TFIIIC may also demarcate heterochromatin in C. elegans.

中文翻译：

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转录独立的TFIIIC绑定站点聚集在秀丽隐杆线虫的层相关域内异染色质边界附近。

背景技术染色质组织对于精确控制基因表达至关重要。在各种真核物种中，普遍的顺式-染色质相互作用域界定了基因组的功能域。然而，在线虫秀丽隐杆线虫中，普遍的染色质接触域限于剂量补偿的性染色体，使得秀丽隐杆线虫染色质组织的原理不清楚。转录因子III C（TFIIIC）是RNA聚合酶III的基础转录因子复合物，与染色质组织有关。没有RNA聚合酶III共同参与的TFIIIC结合（称为额外TFIIIC结合）与酵母，果蝇和哺乳动物细胞中绝缘的活性和非活性染色质结构域有关。是否存在额外的TFIIIC位点并有助于C中的染色质组织。线虫仍然未知。结果我们确定了504条TFIIIC结合位点，该位点在秀丽隐杆线虫胚胎中不存在RNA聚合酶III，而TATA结合蛋白的额外TFIIIC位点共同占据。额外的TFIIIC位点构成了基因组中所有已识别的TFIIIC结合位点的一半。TFIIIC以外的位点在顺式形成密集的簇。额外的TFIIIC位点的簇在常染色体的远端臂域中高度过量表达，常染色体的远端臂域呈现出高水平的异染色质相关组蛋白H3K9三甲基化（H3K9me3）。此外，额外的TFIIIC群集被嵌入在与层相关的域中。尽管存在额外的TFIIIC位点的异染色质环境，但额外的TFIIIC位点的单个簇没有并位于单个H3K9me3标记的区域附近。结论额外的TFIIIC位点簇普遍存在于秀丽隐杆线虫常染色体的臂域中，靠近H3K9me3标记的区域的外边界。鉴于据报道酵母中异染色质绝缘中存在额外的TFIIIC位点活性，我们的观察结果提出了TFIIIC也可能在秀丽隐杆线虫中划定异染色质的可能性。