Mickel S, Arena V, Bauer W
Nucleic Acids Res. 1977;4(5):1465-82. doi: 10.1093/nar/4.5.1465.
A series of closed circular (I) plasmid DNAs has been derived from drug resistance factor R12, and the nicked circular (II) and linear (III) derivatives of these molecules prepared by irradiation in the presence of ethidium bromide and by treatment with restriction enzyme EcoRI, respectively. These DNAs encompass the molecular weight range 3.6 to 61 megadaltons. The base compositions range from 45% to 51% (GC) as estimated by buoyant density determinations. The smaller plasmids are significantly less supercoiled (9-10%) than are the larger (12-13%). The gel electrophoretic behavior of the three DNA structural forms was determined as a function of molecular weight in agarose gels of concentrations ranging from 0.7% to 1.6% and at electrophoresis salt concentrations from 0.02 M to 0.08 M sodium acetate. The mobilities of DNAs I and III undergo a reversal relative to each other at a molecular weight which decreases with increasing agarose gel concentration. The molecular weight at which DNA II fails to enter a gel depends upon the ionic strength during electrophoresis but not upon the gel concentration.
一系列闭环（I型）质粒DNA源自耐药因子R12，这些分子的缺口环状（II型）和线性（III型）衍生物分别通过在溴化乙锭存在下照射以及用限制性内切酶EcoRI处理制备。这些DNA的分子量范围为3.6至61兆道尔顿。通过浮力密度测定估计，其碱基组成范围为45%至51%（GC）。较小的质粒超螺旋程度（9 - 10%）明显低于较大的质粒（12 - 13%）。在浓度范围为0.7%至1.6%的琼脂糖凝胶以及电泳盐浓度为0.02 M至0.08 M醋酸钠的条件下，测定了三种DNA结构形式的凝胶电泳行为与分子量的函数关系。DNA I和III的迁移率在一个分子量处相互反转，该分子量随着琼脂糖凝胶浓度的增加而降低。DNA II无法进入凝胶的分子量取决于电泳过程中的离子强度，而不取决于凝胶浓度。
