de Vos W M, Venema G, Canosi U, Trautner T A
Mol Gen Genet. 1981;181(4):424-33. doi: 10.1007/BF00428731.
Only multimeric, and not monomeric forms of B. subtilis plasmids can transform B. subtilis cells (Canosi et al. 1978). This finding prompted us to study the physico-chemical fate of plasmid DNA in transformation. Competent cells of B. subtilis were exposed to either unfractionated preparations or to preparations of multimeric plasmid DNA. Plasmid DNA was re-extracted from such cells and then analyzed by sedimentation and isopycnic centrifugation and also defined by its sensitivity to nuclease S1 degradation. No double-stranded plasmid DNA could be recovered from cells transformed with unfractionated plasmid preparations which contained predominantly monomeric covalently closed circular (CCC) DNA. Re-extracted plasmid DNA was single-stranded, had a molecular weight considerably smaller than monomer length DNA and had been subject to degradation to acid soluble products. However, when transformations were performed with multimeric DNA (constructed by in vitro ligation of linearized pC194 DNA), both double-stranded and partially double-stranded DNA could be recovered in addition to single-stranded DNA. We assume that plasmid DNA is converted to a single-stranded form in transformation, irrespective of its molecular structure. Double-stranded and partially double-stranded DNAs found in transformation with multimeric DNA would be the products of intramolecular annealing.
只有多聚体形式的枯草芽孢杆菌质粒，而非单体形式，才能转化枯草芽孢杆菌细胞（卡诺西等人，1978年）。这一发现促使我们研究转化过程中质粒DNA的物理化学命运。将枯草芽孢杆菌的感受态细胞暴露于未分级的制剂或多聚体质粒DNA制剂中。从这些细胞中重新提取质粒DNA，然后通过沉降和等密度离心进行分析，并通过其对核酸酶S1降解的敏感性来定义。在用主要包含单体共价闭合环状（CCC）DNA的未分级质粒制剂转化的细胞中，无法回收双链质粒DNA。重新提取的质粒DNA是单链的，其分子量明显小于单体长度的DNA，并且已被降解为酸溶性产物。然而，当用多聚体DNA（通过线性化的pC194 DNA的体外连接构建）进行转化时，除了单链DNA外，还可以回收双链和部分双链DNA。我们假设质粒DNA在转化过程中会转化为单链形式，而与其分子结构无关。在用多聚体DNA转化过程中发现的双链和部分双链DNA将是分子内退火的产物。
