切口封闭酶在体外组装核小体样结构。

Germond J E, Rouvière-Yaniv J, Yaniv M, Brutlag D

Proc Natl Acad Sci U S A. 1979 Aug;76(8):3779-83. doi: 10.1073/pnas.76.8.3779.

The four core histones (H2A, H2B, H3, and H4) and DNA were assembled into nucleosome-like particles at physiological ionic strengths either by an extract of chromatin rich in nicking-closing activity or by the purified nicking-closing enzyme itself. When histone-DNA complexes were assembled in vitro from relaxed circular DNA, nearly physiological numbers of superhelical turns were induced in the DNA molecule. Electron microscopy of the complexes assembled by the chromatin extract revealed a beaded structure and a reduction of the contour length compared to free DNA. Micrococcal nuclease digestion of the histone-DNA complexes yielded 145-base-pair DNA fragments typical of nucleosome core particles and shorter subnucleosomal DNA fragments of discrete length.

四种核心组蛋白（H2A、H2B、H3和H4）与DNA在生理离子强度下组装成核小体样颗粒，这一过程可通过富含切口封闭活性的染色质提取物或纯化的切口封闭酶本身来实现。当从松弛的环状DNA体外组装组蛋白-DNA复合物时，DNA分子中会诱导出接近生理数量的超螺旋圈。对由染色质提取物组装的复合物进行电子显微镜观察，发现其呈串珠状结构，与游离DNA相比，轮廓长度缩短。用微球菌核酸酶消化组蛋白-DNA复合物，产生了145个碱基对的典型核小体核心颗粒DNA片段以及离散长度的较短亚核小体DNA片段。