Crothers D M, Dattagupta N, Hogan M, Klevan L, Lee K S
Biochemistry. 1978 Oct 17;17(21):4525-33. doi: 10.1021/bi00614a026.
We report transient electric dichroism experiments on nucleosomal core particles containing 140 and 175 base pairs of DNA, and on spacerless dinucleosomes. The results indicate that all particles posses a permanent dipole moment. The orientation time of 140 base pair nucleosomes implies an estimated maximum dimension of a = 130 A (a must be at least 111 A), consistent with the disk model. The maximum dimension of the spacerless dinucleosome is estimated to be about 290 A (at least 180 A), ruling out a structure in which two disks are stacked directly on top of each other. The reduced dichroism amplitude indicate that the DNA superhelix axis in nucleosomes aligns perpendicular to the electric field, as expected for a dipole moment directed along a C2 symmetry axis across the disk diameter. Nucleosomes containing 175 base pairs of DNA show a substantially larger dichroism amplitude that do 140 base pair nucleosomes. In the context of the disk model, this result is shown to be consistent with 100 base pairs of DNA per superhelical turn, but not with 80 base pairs per turn.
我们报道了对含有140和175个碱基对DNA的核小体核心颗粒以及无间隔二聚核小体进行的瞬态电二色性实验。结果表明，所有颗粒都具有永久偶极矩。140碱基对核小体的取向时间意味着估计最大尺寸a = 130埃（a必须至少为111埃），这与盘状模型一致。无间隔二聚核小体的最大尺寸估计约为290埃（至少180埃），排除了两个盘直接堆叠在一起的结构。降低的二色性幅度表明，核小体中的DNA超螺旋轴与电场垂直排列，正如沿着穿过盘直径的C2对称轴方向的偶极矩所预期的那样。含有175个碱基对DNA的核小体显示出比140碱基对核小体大得多的二色性幅度。在盘状模型的背景下，这一结果表明与每超螺旋圈100个碱基对的DNA一致，但与每圈80个碱基对不一致。
