Marquet R, Favazza M, Koch M H, Houssier C
Laboratoire de Chimie Macromoléculaire et Chimie Physique, Université de Liège, Belgium.
FEBS Lett. 1990 Mar 12;262(1):131-4. doi: 10.1016/0014-5793(90)80171-e.
The electric linear dichroism of chicken erythrocyte chromatin has been measured as a function of NaCl concentration in the 1-28 mM ionic strength range, using a specially designed Kerr cell with reduced pathlength, and thus, smaller electrode surface. This allowed the determination of the dichroism of compact chromatin in conditions where artifacts due to possible contribution from turbidity are avoided, which was not the case for previous studies in the presence of di- or multivalent cations. The linear dichroism of compact chromatin was found to be positive, as expected from models of the 30-nm fibre in which the linker DNA runs perpendicular to the fibre axis. The dependence of the relaxation times on ionic strength reveals that the process of compaction is first accompanied by an increase in flexibility of the chain followed by a decrease, in the range of 5-10 mM NaCl, and a further decrease above 10 nM NaCl, corresponding to the compaction of the 30 nm fibre.
使用经过特殊设计、光程较短且电极表面较小的克尔盒，在1-28 mM离子强度范围内测量了鸡红细胞染色质的电线性二色性与NaCl浓度的关系。这样就能在避免因浊度可能产生的伪影的条件下测定紧密染色质的二色性，而之前在二价或多价阳离子存在的情况下进行的研究并非如此。正如30纳米纤维模型所预期的那样，紧密染色质的线性二色性为正，其中连接DNA垂直于纤维轴延伸。弛豫时间对离子强度的依赖性表明，在5-10 mM NaCl范围内，压缩过程首先伴随着链柔韧性的增加，随后降低，而在10 nM NaCl以上则进一步降低，这与30纳米纤维的压缩相对应。
