Dimitrov S I, Smirnov I V, Makarov V L
Mol Biol (Mosk). 1987 Sep-Oct;21(5):1400-10.
The optical anisotropy of chromatin with different length of the linker DNA isolated from a variety of sources (Friend erythroleukemia cells, calf thymus, hen erythrocytes and sea urchin sperm) has been studied in a large range of mono- and bivalent cations by the use of flow linear dichroism and electric dichroism. We have found that all chromatins studied displayed negative LD values in the range of 0.25 mM EDTA--2 mM NaCl and close positive values in the range of 2-100 mM NaCl. Mg2+ cations, in contrast to Na+ cations, induce optically isotropic chromatin fibers. All chromatin samples exhibit positive form effect amounting to 5-10% of LD amplitude observed at 260 nm. This form effect is determined by the anisotropic scattering of polarized light by single chromatin fibers. The conformational transition at 2 mM NaCl leads to the distortion of chromatin filament structure. The reversibility of this distortion depends on the length of the linker DNA--for chromatins with linker DNA 10-30 b.p. it is partially reversible, while for preparations with longer linker DNA it is irreversible. Relatively low electric fields do not have an effect on chromatin structure, while higher electric fields (more than 7 kV/cm) distort the structure of chromatin.
利用流动线性二色性和电场二色性，在多种单价和二价阳离子的较大范围内，研究了从多种来源（Friend红白血病细胞、小牛胸腺、鸡红细胞和海胆精子）分离出的具有不同连接DNA长度的染色质的光学各向异性。我们发现，所有研究的染色质在0.25 mM EDTA至2 mM NaCl范围内显示负的LD值，在2至100 mM NaCl范围内显示接近正的值。与Na+阳离子相反，Mg2+阳离子诱导光学各向同性的染色质纤维。所有染色质样品均表现出正的形态效应，其大小相当于在260 nm处观察到的LD振幅的5-10%。这种形态效应由单个染色质纤维对偏振光的各向异性散射决定。在2 mM NaCl时的构象转变导致染色质细丝结构的扭曲。这种扭曲的可逆性取决于连接DNA的长度——对于连接DNA为10-30碱基对的染色质，它是部分可逆的，而对于连接DNA较长的制剂，它是不可逆的。相对较低的电场对染色质结构没有影响，而较高的电场（超过7 kV/cm）会使染色质结构变形。
