Bertrand-Burggraf E, Schnarr M, Lefevre J F, Daune M
Nucleic Acids Res. 1984 Oct 25;12(20):7741-52. doi: 10.1093/nar/12.20.7741.
Supercoiling of DNA is now known to have considerable effects on transcription in bacteria. By abortive initiation reaction (6) we have determined the binding constant KB and the forward rate of isomerization k2 as a function of temperature, pH and buffer for the tet promoter in a supercoiled plasmid. If the activation energy of isomerization is very similar to that obtained previously under the same conditions on a linearized plasmid (6) (respectively 21 +/- 5 kcal/mole and 13 +/- 5 kcal/mole) the supercoiling introduces very important and not well understood changes in the thermodynamic parameters of the association polymerase - promoter. Using the technique of superhelical DNA relaxation by eukaryotic topoisomerase I, we have determined the specific unwinding by RNA polymerase of the tet promoter of pBR322 (430 degrees). This unwinding differs only slightly from the mean value (470 degrees) obtained for all the promoters of pBR322.
现在已知DNA超螺旋对细菌中的转录有相当大的影响。通过流产起始反应（6），我们确定了超螺旋质粒中tet启动子的结合常数KB和异构化正向速率k2作为温度、pH值和缓冲液的函数。如果异构化的活化能与之前在相同条件下在线性化质粒上获得的活化能非常相似（6）（分别为21±5千卡/摩尔和13±5千卡/摩尔），那么超螺旋会在聚合酶-启动子结合的热力学参数中引入非常重要且尚未完全理解的变化。使用真核拓扑异构酶I使超螺旋DNA松弛的技术，我们确定了RNA聚合酶对pBR322（430°）的tet启动子的特异性解旋。这种解旋与pBR322所有启动子获得的平均值（470°）仅略有不同。
