Bloch S, Cedar H
Nucleic Acids Res. 1976 Jun;3(6):1507-19. doi: 10.1093/nar/3.6.1507.
E. coli DNA methylase has been used to methylate chromatin DNA in vitro. At saturation only 50% of the chromatin DNA becomes methylated. The methylated regions of chromatin correspond to that fraction of the chromatin which is sensitive to staphylococcal nuclease. Using in vitro methylated chromatin followed by nuclease digestion movement of chromatin proteins along the DNA can be detected. By this criterion, sonication of chromatin or precipitation with MnCl2 causes 10% of the previously uncovered methylated regions to become covered by protein. Reconstitution of methylated chromatin results in the randomization of the chromatin proteins. Using nuclei which were methylated in vitro we have demonstrated that a small degree of protein sliding does occur during the preparation of chromatin from nuclei. Finally, we have prepared open region DNA by polylysine titration. This procedure does not cause displacement of chromatin proteins.
大肠杆菌DNA甲基化酶已被用于在体外使染色质DNA甲基化。在饱和状态下，只有50%的染色质DNA被甲基化。染色质的甲基化区域对应于对葡萄球菌核酸酶敏感的那部分染色质。使用体外甲基化的染色质，随后进行核酸酶消化，可以检测到染色质蛋白沿DNA的移动。根据这一标准，染色质的超声处理或用MnCl2沉淀会使10%以前未被覆盖的甲基化区域被蛋白质覆盖。甲基化染色质的重建导致染色质蛋白随机分布。使用体外甲基化的细胞核，我们已经证明在从细胞核制备染色质的过程中确实会发生一定程度的蛋白质滑动。最后，我们通过聚赖氨酸滴定制备了开放区域DNA。这个过程不会导致染色质蛋白的移位。
