Packaging without nucleosomes The fundamental compaction of DNA in chromosomes is thought to start with the wrapping of DNA around nucleosomes, but is nucleosome wrapping required for the condensation of mitotic chromosomes? Shintomi et al. combined Xenopus egg extracts and mouse sperm nuclei and found that chromosome-like structures could be assembled in the near-complete absence of nucleosomes (see the Perspective by Kakui and Uhlmann). These “nucleosome-depleted” chromosomes were composed of condensin-enriched discrete axes and poorly organized chromatin loops. This finding challenges the textbook view of mitotic chromosome organization. Science, this issue p. 1284; see also p. 1233 Mitotic-like chromosomes with condensin-containing axes can be assembled in the near-absence of nucleosomes. The nucleosome is the fundamental structural unit of eukaryotic chromatin. During mitosis, duplicated nucleosome fibers are organized into a pair of rod-shaped structures (chromatids) within a mitotic chromosome. However, it remains unclear whether nucleosome assembly is indeed an essential prerequisite for mitotic chromosome assembly. We combined mouse sperm nuclei and Xenopus cell-free egg extracts depleted of the histone chaperone Asf1 and found that chromatid-like structures could be assembled even in the near absence of nucleosomes. The resultant “nucleosome-depleted” chromatids contained discrete central axes positive for condensins, although they were more fragile than normal nucleosome-containing chromatids. Combinatorial depletion experiments underscored the central importance of condensins in mitotic chromosome assembly, which sheds light on their functional cross-talk with nucleosomes in this process.

中文翻译：

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尽管非洲爪蟾卵提取物中的核小体耗尽，但有丝分裂染色体组装

没有核小体的包装 染色体中 DNA 的基本压缩被认为是从 DNA 包裹核小体开始的，但是核小体包裹是否需要有丝分裂染色体的凝聚？Shintomi 等。结合非洲爪蟾卵提取物和小鼠精子核，发现在几乎完全没有核小体的情况下可以组装染色体样结构（参见 Kakui 和 Uhlmann 的观点）。这些“核小体耗尽”的染色体由富含凝聚素的离散轴和组织不良的染色质环组成。这一发现挑战了有丝分裂染色体组织的教科书观点。科学，这个问题 p。1284; 另见第。在几乎没有核小体的情况下，可以组装 1233 条含有凝聚蛋白的轴的有丝分裂样染色体。核小体是真核生物染色质的基本结构单元。在有丝分裂期间，复制的核小体纤维在有丝分裂染色体内被组织成一对杆状结构（染色单体）。然而，尚不清楚核小体组装是否确实是有丝分裂染色体组装的必要先决条件。我们将小鼠精子核和缺乏组蛋白伴侣 Asf1 的非洲爪蟾无细胞卵提取物结合起来，发现即使在几乎没有核小体的情况下也可以组装染色单体样结构。由此产生的“核小体耗尽”染色单体包含离散的中心轴，对凝聚蛋白呈阳性，尽管它们比正常的含有核小体的染色单体更脆弱。组合耗竭实验强调了凝聚素在有丝分裂染色体组装中的核心重要性，