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首页> 外文期刊>Biochemistry >Irregular orientation of nucleosomes in the well-defined chromatin plates of metaphase chromosomes
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Irregular orientation of nucleosomes in the well-defined chromatin plates of metaphase chromosomes

机译：明确定义的中期染色体染色质板中核小体的不规则取向

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In previous studies with partially denatured metaphase chromosomes, we detected platelike structures instead of the chromatin fibers currently considered in different structural models for chromosomes. Here we have observed that dilution of compact metaphase chromosomes with hyposmotic solutions can transform whole chromatids into extended plates formed by many layers. Since this treatment is soft and it does not change the ionic conditions, these observations indicate that native chromosomes are formed by stacked plates. This strengthens our hypothesis about the multilayer structure of chromosomes, which was originally based on results obtained using stronger denaturing conditions. We have investigated the structure of plates emanated from chromosomes using electron tomography. Our three-dimensional reconstructions demonstrate conclusively that the surface of the plates is very smooth and do not show repetitive structures supporting any regular organization of nucleosomes; even the nucleosomes in plate edges show irregular orientations. Furthermore, we have used polarizing microscopy for the study of whole chromosomes in metaphase cells in aqueous solution. Our results show that condensed chromosomes are not birefringent under structuring ionic conditions similar to those used with plates. This observation is incompatible with the existence of parallel columns of nucleosomes within chromosomes. In summary, we have not detected any regular orientation of nucleosomes, but at the same time, our results indicate that the bulk of chromatin in native chromosomes is organized forming very well-defined plates, in which the nucleosomes of the successive layers are interdigitated. Presumably, this dense structure is required for safe transfer of DNA to daughter cells.
机译：在先前使用部分变性中期染色体的研究中，我们检测到了板状结构，而不是当前在不同染色体结构模型中考虑的染色质纤维。在这里我们已经观察到，用低渗溶液稀释紧密中期染色体可以将整个染色单体转化成由许多层组成的延伸板。由于这种处理是柔软的，并且不会改变离子条件，因此，这些观察结果表明天然染色体是由堆叠的板形成的。这加强了我们关于染色体多层结构的假设，该假设最初是基于使用更强变性条件获得的结果。我们已经研究了使用电子断层扫描从染色体发出的板的结构。我们的三维重建最终证明了板的表面非常光滑，并且没有显示出支持核糖体任何规则组织的重复结构。即使板边缘的核小体也显示不规则的方向。此外，我们已经使用偏光显微镜研究了水溶液中中期细胞的整个染色体。我们的结果表明，在结构化离子条件下，浓缩染色体在双板条件下不是双折射的。该观察结果与染色体内核小体平行柱的存在不相容。总而言之，我们没有检测到核小体的任何规则取向，但是同时，我们的结果表明，天然染色体中的大部分染色质组织良好，形成了非常清晰的板块，其中连续层的核小体相互交叉。据推测，这种紧密的结构是将DNA安全转移到子细胞所必需的。

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