Debabov V G, Azizbekian R R, Khlebalina O I, D'iachenko V V, Galushka F P
Genetika. 1977;13(3):496-501.
Centrifugation of Bacillus thuringiensis 351 DNA in CsCl-ethidium bromide density gradient has revealed, besides the main band of chromosomal DNA (p = 1.56 g/cm2), some additional bands with higher density, which usually correspond cicle superhelix DNAs, are revealed. 6 discrete bands are observed under electrophoresis of total fraction of minor DNA bands, which suggests, that the preparation contains cicle DNAs of different size. The treatment with DNAse results in the appearance of 3 bands corresponding to opened cicle DNA forms, their molecular weight being 12-10(6)--4-10(6) daltons. Cicle super-helix and opened cicle DNA forms are found in minor fraction by means of electrone microscopy. Statistical analysis has revealed the presence of at least three types of cicle molecules of different size. The variant 351-10, free of extrachromosomal elements, is isolated after ethidium bromide treatment at high temperature. Possible mechanisms of cicle DNAs formation are discussed. Biological function of DNA extrachromosomes fragments in Bacillus thuringiensis is still obscure.
苏云金芽孢杆菌351 DNA在氯化铯-溴化乙锭密度梯度中的离心显示，除了染色体DNA的主带（p = 1.56 g/cm²）外，还发现了一些密度更高的附加带，这些带通常对应于环状超螺旋DNA。在次要DNA带的总级分电泳中观察到6条离散带，这表明该制剂含有不同大小的环状DNA。用DNA酶处理会产生3条对应于开放环状DNA形式的带，它们的分子量为12 - 10⁶ - 4 - 10⁶道尔顿。通过电子显微镜在次要级分中发现了环状超螺旋和开放环状DNA形式。统计分析表明存在至少三种不同大小的环状分子类型。变体351 - 10在高温下经溴化乙锭处理后分离出来，不含染色体外元件。文中讨论了环状DNA形成的可能机制。苏云金芽孢杆菌中DNA染色体外片段的生物学功能仍然不清楚。
