【摘要】 在拓扑异构酶Ⅰ缺失的大肠杆菌突变株中,抑制转录和翻译可以消除高度负超螺旋.为了检测起作用的拓扑异构酶,在拓扑异构酶Ⅰ缺陷的菌株中,以萘啶酮酸抑制旋转酶和拓扑异构酶Ⅳ的活性,结果表明并未影响高度负超螺旋的消除.进一步作了拓扑异构酶Ⅰ,旋转酶,拓扑异构酶Ⅲ和拓扑异构酶Ⅳ的体外松弛实验,结果表明,拓扑异构酶Ⅲ可以松弛高度负超螺旋到正常的超螺旋水平.可以认为拓扑异构酶Ⅲ负责松弛高度负超螺旋并受到某种信号机制的调控.更多还原

【Abstract】 Inhibition of transcription and translation could both eliminate hypernegatively supercoiled plasmid pBR322 DNA in E.coli topA mutants.To examine which topoisomerase was due to the relaxation of hypernegative supercoiling,inhibition of gyrase and topoisomeraseⅣwith nalidixic acid in vivo was proved to have no effect on the relaxation.Furthermore,the relaxing activity of topoisomeraseⅠ,gyrase,topoisomeraseⅡand topoisomeraseⅣwas assayed in vitro.And the results indicated that topoisomeraseⅢrelaxed the hypernegatively supercoiled plasmid DNA but not the normal plasmid in vitro.So,we hypothesized that topoisomeraseⅢwas responsible for the relaxation of excess supercoiling in E.coli topA mutants and that there might be some signal system promoting and controlling the relaxing activity of topoisomeraseⅢ.更多还原