Bonilla P J, Freytag S O, Lutter L C
Molecular Biology Research Program, Henry Ford Hospital, Detroit, MI 48202.
Nucleic Acids Res. 1991 Jul 25;19(14):3965-71. doi: 10.1093/nar/19.14.3965.
It has been proposed that transcriptionally active chromatin contains totally unconstrained supercoiling. The results of recent studies have raised the possibility that this topological state is the property of highly transcribed genes. Since the transcription rate of RNA polymerase II genes can be dramatically increased by the presence of an enhancer, we have determined if the transcription complex of an enhancer-activated plasmid contains totally unconstrained supercoils. Following transfection into COS7 cells, the topology of the transcription complex DNA was determined directly by agarose gel electrophoresis. We find that an enhancer-activated plasmid transcription complex is supercoiled, and these supercoils remain following topoisomerase I treatment. Thus the transcribing complexes contain constrained supercoils, and the level of supercoiling suggests a nucleosome-like organization. However, we cannot rule out the possibility that unconstrained supercoils exist in addition to these constrained supercoils in the transcription complex in the cell.
有人提出转录活性染色质含有完全无约束的超螺旋。最近的研究结果提出了这种拓扑状态是高度转录基因的特性的可能性。由于增强子的存在可显著提高RNA聚合酶II基因的转录速率，我们已确定增强子激活质粒的转录复合物是否含有完全无约束的超螺旋。转染到COS7细胞后，通过琼脂糖凝胶电泳直接确定转录复合物DNA的拓扑结构。我们发现增强子激活的质粒转录复合物是超螺旋的，并且这些超螺旋在拓扑异构酶I处理后仍然存在。因此，转录复合物含有受约束的超螺旋，超螺旋水平表明存在类似核小体的组织。然而，我们不能排除在细胞中转录复合物中除了这些受约束的超螺旋之外还存在无约束超螺旋的可能性。
