Tetrameric structure of centromeric nucleosomes in interphase Drosophila cells.
Tetrameric structure of centromeric nucleosomes in interphase Drosophila cells.
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DOI：
10.1371/journal.pbio.0050218
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发表时间：
2007-08
期刊：
影响因子：
9.8
通讯作者：
Henikoff S
中科院分区：
文献类型：
--
作者：
Dalal Y;Wang H;Lindsay S;Henikoff S
着丝粒是一种特殊的染色质结构，在有丝分裂时负责染色体的平等分离，由着丝粒特异性组蛋白H3变体（CenH 3）表观遗传维持。然而，着丝粒维持的机制基础是未知的。我们研究了果蝇细胞CenH 3核小体的生化特性。CenH 3核小体的交联鉴定了各自含有CenH 3、H2 A、H2 B和H4的一个拷贝的异型四聚体。间期CenH 3颗粒显示约120个DNA碱基对的稳定缔合。纯化的着丝粒核小体阵列具有典型的“串珠”的外观，通过电子显微镜，但似乎在生理条件下抵抗凝聚。原子力显微镜显示，天然CenH 3-含有核小体只有一半高的规范八聚体核小体，确认通过交联检测到的四聚体结构包括整个相间核小体颗粒。这种稳定的半核小体在体内的演示提供了一个可能的基础，沉积在常染色质区域，这可能有助于维持着丝粒的身份着丝粒核小体的不稳定性。核小体的八聚体结构被普遍认为是染色质的基本单位。这当然是大部分核小体的情况下，然而，还没有报道与着丝粒相关的核小体的体内结构。虽然着丝粒只占基因组景观的一小部分，但它们在有丝分裂期间分离染色体的作用对于维持基因组完整性至关重要。我们报告的表征着丝粒染色质从果蝇细胞，使用详细的生化，电子显微镜和原子力显微镜分析。令人惊讶的是，我们发现，与大量染色质形成鲜明对比的是，着丝粒核小体在体内是稳定的异型四聚体，其中CenH 3（着丝粒特异性H3变体），H2 A，H2 B和H4各有一个拷贝，在间期（细胞周期的细胞生长期）包裹一整圈DNA。这导致核小体颗粒只有本体核小体的一半高。这些意想不到的发现可以帮助解释含有CenH 3的核小体的动态行为，即它们杂乱地沉积，但在非着丝粒区域翻转。我们证明了在着丝粒处存在稳定的半核小体，这表明了一种维持着丝粒身份的新机制。果蝇的着丝粒核小体是组蛋白四聚体，而不是染色质其余部分的典型八聚体。这种前所未有的稳定半核小体的排列可能有助于维持着丝粒的同一性。
Centromeres, the specialized chromatin structures that are responsible for equal segregation of chromosomes at mitosis, are epigenetically maintained by a centromere-specific histone H3 variant (CenH3). However, the mechanistic basis for centromere maintenance is unknown. We investigated biochemical properties of CenH3 nucleosomes from Drosophila melanogaster cells. Cross-linking of CenH3 nucleosomes identifies heterotypic tetramers containing one copy of CenH3, H2A, H2B, and H4 each. Interphase CenH3 particles display a stable association of approximately 120 DNA base pairs. Purified centromeric nucleosomal arrays have typical “beads-on-a-string” appearance by electron microscopy but appear to resist condensation under physiological conditions. Atomic force microscopy reveals that native CenH3-containing nucleosomes are only half as high as canonical octameric nucleosomes are, confirming that the tetrameric structure detected by cross-linking comprises the entire interphase nucleosome particle. This demonstration of stable half-nucleosomes in vivo provides a possible basis for the instability of centromeric nucleosomes that are deposited in euchromatic regions, which might help maintain centromere identity. The octameric structure of eukaryotic nucleosomes is universally accepted as the basic unit of chromatin. This is certainly the case for the vast bulk of nucleosomes; however, there have been no reports of the in vivo structure of nucleosomes associated with centromeres. Though centromeres make up only a minute fraction of the genomic landscape, their role in segregating chromosomes during mitosis is essential for maintaining genomic integrity. We report the characterization of centromeric chromatin from Drosophila cells, using detailed biochemical, electron microscopic, and atomic force microscopic analyses. Surprisingly, we found that, in striking contrast to bulk chromatin, centromeric nucleosomes are stable heterotypic tetramers in vivo, with one copy of CenH3 (the centromere-specific H3 variant), H2A, H2B, and H4 each, wrapping one full turn of DNA at interphase (the cell growth phase of the cell cycle). This results in nucleosome particles that are only half as high as bulk nucleosomes. These unexpected findings can help account for the dynamic behavior of CenH3-containing nucleosomes, whereby they are deposited promiscuously but are turned over in noncentromeric regions. Our demonstration of the existence of stable half-nucleosomes at centromeres suggests a novel mechanism for maintaining centromere identity. The centromeric nucleosomes of Drosophila are histone tetramers rather than the canonical octomer of the rest of chromatin. This unprecedented arrangement of stable half-nucleosomes might help maintain centromere identity.
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DOI：
10.1083/jcb.200701065
发表时间：
2007-03-12
期刊：
The Journal of cell biology
影响因子：
--
作者：
Maddox PS;Hyndman F;Monen J;Oegema K;Desai A
通讯作者：
Desai A
DOI：
10.1073/pnas.172403699
发表时间：
2002-12-10
影响因子：
11.1
作者：
Ahmad, K;Henikoff, S
通讯作者：
Henikoff, S
影响因子：
1.6
作者：
McEwen, BF;Hsieh, CE;Rieder, CL
通讯作者：
Rieder, CL
影响因子：
7.8
作者：
Jansen, Lars E. T.;Black, Ben E.;Foltz, Daniel R.;Cleveland, Don W.
通讯作者：
Cleveland, Don W.
影响因子：
4
作者：
Nakashima, H;Nakano, M;Masumoto, H
通讯作者：
Masumoto, H