Okada K, Ohta T, Hirose S
DNA Research Center, National Institute of Genetics, Shizuoka.
J Biochem. 1991 Feb;109(2):365-9.
In the presence of a molar excess of eukaryotic DNA topoisomerase II and an appropriate concentration of dextran sulfate, relaxed closed circular DNA is converted to a negatively supercoiled form. The reaction is dependent on ATP. Neither adenosine 5'-[beta,gamma-imido]-triphosphate nor adenosine 5'-[gamma-thio]triphosphate can substitute for ATP. The negative supercoils formed are relaxed by subsequent addition of DNA topoisomerase I to the supercoiling reaction mixture. Covalent closure of a nicked circular DNA in the presence of DNA topoisomerase II and dextran sulfate but in the absence of ATP causes a small decrease in the linking number. These results suggest that when an appropriate concentration of dextran sulfate is present, the binding of a molar excess of eukaryotic DNA topoisomerase II constrains a small number of negative supercoils in DNA, which in turn generate unconstrained negative supercoils at the expense of ATP.
在存在摩尔过量的真核生物DNA拓扑异构酶II和适当浓度的硫酸葡聚糖的情况下，松弛的闭环DNA会转变为负超螺旋形式。该反应依赖于ATP。腺苷5'-[β,γ-亚氨基]三磷酸和腺苷5'-[γ-硫代]三磷酸均不能替代ATP。通过随后向超螺旋反应混合物中添加DNA拓扑异构酶I，可使形成的负超螺旋松弛。在存在DNA拓扑异构酶II和硫酸葡聚糖但不存在ATP的情况下，带切口的环状DNA的共价闭合会导致连环数略有减少。这些结果表明，当存在适当浓度的硫酸葡聚糖时，摩尔过量的真核生物DNA拓扑异构酶II的结合会在DNA中限制少量负超螺旋，而这些负超螺旋又会以ATP为代价产生无约束的负超螺旋。
