Wu H Y, Shyy S H, Wang J C, Liu L F
Department of Biological Chemistry, Johns Hopkins School of Medicine, Baltimore, Maryland 21205.
Cell. 1988 May 6;53(3):433-40. doi: 10.1016/0092-8674(88)90163-8.
We show that transcription of a DNA molecule inside a bacterium is accompanied by local and temporal supercoiling of the DNA template: as transcription proceeds, DNA in front of the transcription ensemble becomes positively supercoiled, and DNA behind the ensemble becomes negatively supercoiled. Because bacterial gyrase and topoisomerase I act differently on positively and negatively supercoiled DNA, the formation of twin supercoiled domains during transcription is manifested by a large increase or decrease in the linking number of an intracellular plasmid when bacterial DNA gyrase or topoisomerase I, respectively, is inhibited. Such changes in linking number are strongly dependent on transcription of the plasmid in cis and on the relative orientations of transcription units on the plasmid. These results indicate that the state of supercoiling of bacterial DNA is strongly modulated by transcription, and that DNA topoisomerases are normally involved in the elongation step of transcription.
我们发现，细菌内DNA分子的转录伴随着DNA模板的局部和瞬时超螺旋化：随着转录的进行，转录复合体前方的DNA形成正超螺旋，而复合体后方的DNA形成负超螺旋。由于细菌的促旋酶和拓扑异构酶I对正、负超螺旋DNA的作用不同，当分别抑制细菌DNA促旋酶或拓扑异构酶I时，转录过程中双超螺旋结构域的形成表现为细胞内质粒连接数的大幅增加或减少。连接数的这种变化强烈依赖于顺式质粒的转录以及质粒上转录单元的相对方向。这些结果表明，细菌DNA的超螺旋状态受到转录的强烈调控，并且DNA拓扑异构酶通常参与转录的延伸步骤。
