Shishido K
J Biochem. 1979 Sep;86(3):711-7. doi: 10.1093/oxfordjournals.jbchem.a132575.
Covalently closed-circular, superhelical DNAs, including viral DNAs, bacterial plasmid DNAs, and bacteriophage replicative-form DNA, were treated with a small amount of Haemophilus gallinarum DNA-relaxing enzyme to generate incompletely relaxed DNA molecules. Each sample consisted of a set of closed-circular DNA molecules differing by one turn in their number of superhelical turns. The DNA samples were analyzed by agarose gel electrophoresis under conditions such that the electrophoretic mobility was a function of the number of turns. The numbers of superhelical turns (at 37 degrees C in 20 mM Tris-HCl (pH 7.5)-5 mM MgCl2) in the DNAs of pSC101 (5.8 megadaltons), Colicin E1 (4.2 megadaltons), pMR4 (4.0 megadaltons; recombinant between pBR322 and lambda DNA fragment), phi X174 replicative-form (RF) I, Simian virus 40 (SV40), and polyoma virus (3.4--3.6 megadaltons each), and lambda dv021 (2.05 megadaltons) were estimated to be 36, 27, 23--24, 20--21, 20--21, 20--21, and 11--13, respectively. It appears that the number of superhelical turns is mainly a function of the molecular weight of the DNA, at least in the substrates tested here.
共价闭合环状超螺旋DNA，包括病毒DNA、细菌质粒DNA和噬菌体复制型DNA，用少量鸡嗜血杆菌DNA松弛酶处理以产生不完全松弛的DNA分子。每个样品由一组超螺旋匝数相差一圈的闭合环状DNA分子组成。在电泳迁移率是匝数函数的条件下，通过琼脂糖凝胶电泳分析DNA样品。pSC101（5.8兆道尔顿）、大肠杆菌素E1（4.2兆道尔顿）、pMR4（4.0兆道尔顿；pBR322与λDNA片段之间的重组体）、φX174复制型（RF）I、猴病毒40（SV40）和多瘤病毒（各3.4 - 3.6兆道尔顿）以及λdv021（2.05兆道尔顿）的DNA在20 mM Tris - HCl（pH 7.5）- 5 mM MgCl2中于37℃时的超螺旋匝数估计分别为36、27、23 - 24、20 - 21、20 - 21、20 - 21和11 - 13。至少在这里测试的底物中，超螺旋匝数似乎主要是DNA分子量的函数。
