Structure and phase diagram of nucleosome core particles aggregated by multivalent cations
Structure and phase diagram of nucleosome core particles aggregated by multivalent cations
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DOI：
10.1529/biophysj.107.108365
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发表时间：
2007-11-01
影响因子：
3.4
通讯作者：
Livolant, Francoise
中科院分区：
文献类型：
--
作者：
Bertin, Aurelie;Mangenot, Stephanie;Livolant, Francoise
真核细胞染色质在体内和体外的致密化程度对离子环境高度敏感。我们讨论了多价离子对染色质结构单元--核小体核心粒子(NCP)的相互作用和相互组织的影响。探索、比较和讨论了在10 mM Tris缓冲液和不同量的镁(镁)或亚精胺(Spd(3+))存在下NCPs的沉淀条件。此外，还利用冷冻断口电子显微镜、低温电子显微镜和X射线衍射等辅助技术对聚集体的结构进行了分析。在Mg2+-NCP聚集体中，NCP倾向于一个接一个地堆叠在一起，形成不是长期组织的列。在Spd(3+)存在下，NCPs析出形成致密的各向同性相、柱状无序相、二维柱状六方相或三维晶体。更多的有序相(二维或三维六边形)出现在靠近沉淀线的地方，阳离子携带的正电荷数略大于NCP的可用负电荷数。所有有序相与致密的各向同性相共存。过多的聚阳离子阻止了六方相和柱状相的形成。
The degree of compaction of the eukaryotic chromatin in vivo and in vitro is highly sensitive to the ionic environment. We address the question of the effect of multivalent ions on the interactions and mutual organization of the chromatin structural units, the nucleosome core particles (NCPs). Conditions of precipitation of NCPs in the presence of 10 mM Tris buffer and various amounts of either magnesium (Mg2+) or spermidine (Spd(3+)) are explored, compared, and discussed in relation to theoretical models. In addition, the structure of the aggregates is analyzed by complementary techniques: freeze-fracture electron microscopy, cryoelectron microscopy, and x-ray diffraction. In Mg2+-NCP aggregates, NCPs tend to stack on top of one another to form columns that are not long-range organized. In the presence of Spd(3+), NCPs precipitate to form a dense isotropic phase, a disordered phase of columns, a two-dimensional columnar hexagonal phase, or a three-dimensional crystal. The more ordered phases (two-dimensional or three-dimensional hexagonal) are found close to the precipitation line, where the number of positive charges carried by cations is slightly larger than the number of available negative charges of the NCPs. All ordered phases coexist with the dense isotropic phases. Formation of hexagonal and columnar phases is prevented by an excess of polycations.