Odakura Y, Hashimoto H, Mitsuhashi S
J Bacteriol. 1974 Dec;120(3):1260-7. doi: 10.1128/jb.120.3.1260-1267.1974.
The physical characteristics of a mutant, R(M201-2), capable of conferring high and stable ampicillion resistance was analyzed. The R(M201-2) and its parent R-factor deoxyribonucleic acid (DNA) could be isolated as an extrachromosomal and covalently closed circular form. Their buoyant densities were both 1.712 g/cm(3), and their molecular weights were about 82 x 10(6) and 64 x 10(6), respectively, when measured by CsCl and sucrose density gradient analyses. The contour lengths by electron microscopy were 35.9 +/- 0.6 and 31.0 +/- 0.6 mum, respectively. By using the extracted R-factor DNA, the mutant and parent characters were transformable to another Escherichia coli strain. The mutant R factor showed an increased amount of DNA even after conjugal transfer to Proteus. An increase in the size of R-factor DNA was thus considered to be the cause of the high level of ampicillin resistance.
对一种能够赋予高且稳定氨苄西林抗性的突变体R（M201 - 2）的物理特性进行了分析。R（M201 - 2）及其亲本R因子脱氧核糖核酸（DNA）能够以染色体外共价闭合环状形式分离出来。通过氯化铯和蔗糖密度梯度分析测量，它们的浮力密度均为1.712 g/cm³，分子量分别约为82×10⁶和64×10⁶。通过电子显微镜观察，其轮廓长度分别为35.9±0.6和31.0±0.6μm。使用提取的R因子DNA，突变体和亲本性状可转化至另一株大肠杆菌。即使在与变形杆菌进行接合转移后，突变型R因子的DNA量仍有所增加。因此，R因子DNA大小的增加被认为是高水平氨苄西林抗性的原因。
