Kubista M, Härd T, Nielsen P E, Nordén B
Biochemistry. 1985 Nov 5;24(23):6336-42. doi: 10.1021/bi00344a003.
We have studied the structure of nuclease-solubilized chromatin from Ehrlich ascites cells by flow linear dichroism (LD) using the anisotropic absorption of the DNA bases and of two intercalated dyes, ethidium bromide and methylene blue. It is confirmed that intercalation occurs preferentially in the linker part of the chromatin fiber, at binding ratios (dye/base) below 0.020. Using this information, we determined the orientation of the linker in relation to the average DNA organization in chromatin. The LD measurements indicate that the conformation of chromatin is considerably changed in the ionic strength interval 0.1-10 mM NaCl: with increasing salt concentration, the LD of the intrinsic DNA base absorption changes signs, from negative to positive, at approximately 2.5 mM NaCl. The LD of the intercalated dyes also changes signs, however, at a somewhat higher salt concentration. The results are analyzed in terms of possible allowed combinations of tilt angles of nucleosomes and pitch or tilt angles of linker DNA sections relative to the fiber axis, at different salt concentrations in the interval 0.1-10 mM NaCl. Two models for the salt-induced structural change of chromatin are discussed.
我们通过流动线性二色性（LD），利用DNA碱基以及两种插入染料（溴化乙锭和亚甲蓝）的各向异性吸收，研究了艾氏腹水癌细胞中核酸酶溶解染色质的结构。已证实，在染色质纤维的连接区部分，当结合比率（染料/碱基）低于0.020时，优先发生插入。利用这一信息，我们确定了连接区相对于染色质中平均DNA组织的方向。LD测量表明，在0.1 - 10 mM NaCl的离子强度区间内，染色质的构象发生了显著变化：随着盐浓度的增加，固有DNA碱基吸收的LD在约2.5 mM NaCl时改变符号，从负变为正。插入染料的LD也改变符号，不过是在稍高的盐浓度下。在0.1 - 10 mM NaCl区间的不同盐浓度下，根据核小体倾斜角与连接区DNA片段相对于纤维轴的螺距或倾斜角的可能允许组合对结果进行了分析。讨论了染色质盐诱导结构变化的两种模型。
