核小体构象：pH值及有机溶剂的影响
Nucleosome conformation: pH and organic solvent effects.
作者信息
Zama M, Olins D E, Prescott B, Thomas G J
出版信息
Nucleic Acids Res. 1978 Oct;5(10):3881-97. doi: 10.1093/nar/5.10.3881.
Monomer nucleosomes (nu 1) from chicken erythrocyte nuclei were examined in aqueous buffers (8 greater than pH greater than 3) and in solvent mixtures (i.e., water and ethanol, ethylene glycol, dioxane, dimethyl sulfoxide, 2-methyl-2,4-pentanediol, polyethylene glycol, sucrose, or urea). Circular dichroism, laser Raman spectroscopy of nu 1, and the fluorescence of nu 1 labeled with N-(3-pyrene) maleimide on thiol groups of H3 histone were employed to detect conformational transitions in nu 1. The results of pH studies were as follows: 5.5 greater than pH greater than 4.8, suppression of DNA ellipticity and no change of histone alpha-helix; 4.6 greater than pH greater than 4.2 an irreversible increase in the B character of DNA, a slight loss of histone alpha-helix, and a parallel loss of pyrene excimer fluorescence; 4 greater than pH, aggregation of nu 1 and protonation of the DNA bases C and A. Results obtained in the studies of nu 1 in solvent mixtures included the following: sharp conformational transitions that variously involved an increase in the B character of DNA, a slight loss of histone alpha-helix, and a loss of pyrene excimer. Different solvents required different concentrations to effect these conformational changes.
对来自鸡红细胞核的单体核小体（nu 1）在水性缓冲液（8＞pH＞3）以及溶剂混合物（即水与乙醇、乙二醇、二氧六环、二甲基亚砜、2-甲基-2,4-戊二醇、聚乙二醇、蔗糖或尿素）中进行了研究。利用圆二色性、nu 1的激光拉曼光谱以及用N-(3-芘基)马来酰亚胺标记H3组蛋白硫醇基团的nu 1的荧光来检测nu 1中的构象转变。pH研究结果如下：5.5＞pH＞4.8时，DNA椭圆率受到抑制，组蛋白α-螺旋无变化；4.6＞pH＞4.2时，DNA的B型特征不可逆增加，组蛋白α-螺旋略有损失，芘准分子荧光平行损失；pH＜4时，nu 1聚集，DNA碱基C和A质子化。在溶剂混合物中对nu 1进行研究所得结果如下：发生了明显的构象转变，不同程度地涉及DNA的B型特征增加、组蛋白α-螺旋略有损失以及芘准分子损失。不同溶剂需要不同浓度才能实现这些构象变化。
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