Espinás M L, Carballo M
Departamento de Génetica Molecular, Centro de Investigación y Desarrollo (CSIC), Barcelona, Spain.
Plant Mol Biol. 1993 Mar;21(5):847-57. doi: 10.1007/BF00027116.
We have investigated the presence of higher-order chromatin structures in different maize tissues. Taking advantage of the pulsed-field gel electrophoresis technique to analyse large DNA fragments from intact nuclei and cells, we have determined the size distribution of the high-molecular-weight DNA fragments obtained from chromatin degradation by endogenous nucleases in isolated nuclei. Chromatin digestion leads to the appearance of stable DNA fragments of about 50 kb in all the tissues examined, suggesting the folding of DNA in higher-order chromatin domain structures. It has been reported that such chromatin domains are formed by loops of the 30 nm fibers anchored to the nuclear matrix by a complex set of proteins, including DNA topoisomerase II. Treatment of maize protoplasts with the calcium ionophore A23187 and the antitumour drug VM-26, which specifically inhibit the religation of the cleaved DNA in the topoisomerase II reaction, also produces the 50 kb structure. Analysis of the DNA contained in the 50 kb chromatin structure shows a higher degree of methylation than in bulk maize chromosomal DNA. The role of methylated DNA in the chromatin folding is discussed.
我们研究了不同玉米组织中高阶染色质结构的存在情况。利用脉冲场凝胶电泳技术分析来自完整细胞核和细胞的大片段DNA，我们确定了从分离细胞核中内源性核酸酶对染色质降解所获得的高分子量DNA片段的大小分布。在所有检测的组织中，染色质消化都会导致出现约50 kb的稳定DNA片段，这表明DNA在高阶染色质结构域中折叠。据报道，这种染色质结构域是由30 nm纤维的环形成的，这些环通过包括DNA拓扑异构酶II在内的一组复杂蛋白质锚定在核基质上。用钙离子载体A23187和抗肿瘤药物VM - 26处理玉米原生质体，这两种物质会特异性抑制拓扑异构酶II反应中切割DNA的重新连接，也会产生50 kb的结构。对50 kb染色质结构中所含DNA的分析表明，其甲基化程度高于玉米染色体总DNA。文中讨论了甲基化DNA在染色质折叠中的作用。
