Smith S B, Bendich A J
Department of Genetics, University of Washington, Seattle 98195.
Biopolymers. 1990;29(8-9):1167-73. doi: 10.1002/bip.360290807.
Individual ethidium-stained DNA molecules, embedded in an agarose gel made with electrophoresis buffer (0.05 molar salt), are observed using a fluorescence microscope. In the first experiment, open circular 66 kilobase pair (kbp) plasmids, immobilized by agarose fibers threaded through their centers, display entropic "rubber" elasticity. The charged molecules extend in an electric field of several volts per centimeter and contract to a compact random coil when the field is removed. The extension of the plasmids as a function of field strength is consistent with the freely jointed chain model when the effective electrophoretic charge density is set at 15 e-per persistence length. In a second experiment, stained linear 48.5 kbp DNA molecules are observed as random coils immobilized in agarose. A measure of their size, here named the "maximal-X-extent," is taken for 100 molecules and found to average 1.47 mu. A Monte Carlo computer simulation of random coils (freely jointed chain model) gives the same maximal-X-extent value when the persistence length is set at 0.08 mu.
使用荧光显微镜观察嵌入由电泳缓冲液（0.05摩尔盐）制成的琼脂糖凝胶中的单个溴化乙锭染色的DNA分子。在第一个实验中，通过穿过其中心的琼脂糖纤维固定的开环66千碱基对（kbp）质粒表现出熵“橡胶”弹性。带电分子在每厘米几伏的电场中伸展，当电场去除时收缩成紧密的无规线团。当有效电泳电荷密度设定为每持久长度15个电子时，质粒的伸展随场强的变化符合自由连接链模型。在第二个实验中，观察到染色的线性48.5 kbp DNA分子是固定在琼脂糖中的无规线团。对100个分子测量其大小，这里称为“最大X延伸”，发现平均值为1.47微米。当持久长度设定为0.08微米时，无规线团（自由连接链模型）的蒙特卡罗计算机模拟给出相同的最大X延伸值。
