Makarov V L, Dimitrov S I
Mol Biol (Mosk). 1982 Sep-Oct;16(5):1086-96.
The chromatin structure in solution was studied by the flow linear dichroism method (LD) in a wide range of ionic strengths. It was found that the increasing of the ionic strength from 0.25 mM EDTA, pH 7.0 to 100 mM NaCl leads to a manifold decrease of the LD amplitude of chromatin and inversion of the LD sign from negative to positive at 2 mM NaCl. Chromatin exhibits a positive LD maximum value at 10-20 mM NaCl. These data enable us to conclude that in very low ionic strength (0.25 mM EDTA-2mM NaCl) the nucleosome discs are oriented with their flat faces parallel to the chromatin filament axis. Increasing ionic strength up to 20 mM NaCl leads to reorientation of the nucleosome discs and to formation of chromatin structure with nucleosome flat faces more or less perpendicular to the fibril axis. A conformational transition of that kind is not revealed in H1-depleted chromatin. This testifies to the fact that the histone H1 is responsible for the higher order structure of chromatin. It was found that divalent cations do not induce the inversion of the LD sign of chromatin.
采用流动线性二色性方法（LD）在较宽离子强度范围内对溶液中的染色质结构进行了研究。结果发现，离子强度从pH 7.0的0.25 mM EDTA增加到100 mM NaCl时，染色质的LD振幅会大幅降低，并且在2 mM NaCl时LD信号会从负向正反转。染色质在10 - 20 mM NaCl时呈现正的LD最大值。这些数据使我们能够得出结论，在极低离子强度（0.25 mM EDTA - 2 mM NaCl）下，核小体盘以其平面平行于染色质丝轴的方向排列。将离子强度增加到20 mM NaCl会导致核小体盘重新定向，并形成核小体平面或多或少垂直于纤维轴的染色质结构。在H1缺失的染色质中未观察到这种构象转变。这证明组蛋白H1负责染色质的高级结构。研究发现二价阳离子不会诱导染色质LD信号的反转。
