EFFECTS OF DNA SUPERCOILING ON THE TOPOLOGICAL PROPERTIES OF NUCLEOSOMES

在核小体核心颗粒中，至少有145个碱基对的DNA 以超螺旋构象与组蛋白八聚体结合。 我们已经问过这些粒子的存在对 DNA促旋酶超螺旋DNA能力。 合成 微型染色体，通过重组 核心组蛋白与闭环质粒pBR322， 用不同量的DNA促旋酶处理。 我们发现 可以达到的超螺旋的最大水平几乎是 无蛋白质质粒和半饱和质粒相同 与核心组蛋白，即使超螺旋不会导致 组蛋白从复合物中丢失。 看来，在充分 高水平的超螺旋，核心粒子被破坏， 与组蛋白结合的DNA不再受限制。

In the nucleosome core particle, at least 145 base pairs of DNA are bound to the histone octamer in a superhelical conformation. We have asked what effect the presence of these particles has on the ability on DNA gyrase to supercoil DNA. Synthetic minichromosomes, constructed by reconstituting complexes of core histones with the closed circular plasmid pBR322, were treated with various amounts of DNA gyrase. We have found that the maximum level of supercoiling that is attainable is nearly identical for protein-free plasmids and for plasmids half-saturated with core histones, even though supercoiling does not result in a loss of histones from the complex. It appears that, at sufficiently high levels of supercoiling, the core particle is disrupted in such a way that the DNA bound to histones is no longer constrained.