Zverev V V, Vorob'eva I P, Drygin Iu F, Khmel' I A
Genetika. 1982;18(1):56-63.
A fraction of plasmid DNA from K and X colicins producing Escherichia coli K235 cells was studied. Cells of this strain are shown to contain four types of plasmids with molecular weights of 21.6.10(6), 38.8.10(6) daltons. Transformation of E. coli C600 by a total plasmid DNA yielded clones containing a single plasmid - colicinogenic K factor (ColK, a mol wt 4.4.10(6)). ColK DNA is present in cells in a large number of copies, replicates in the presence of chloramphenicol, requires DNA polymerase I. Two fragments with mol wts 3.4 and 1.1.10(6) are formed when ColK DNA is treated with EcoRI enzyme. After circularization using phage T4 DNA ligase, the 3.4.10(6) fragment was capable of autonomous replication and stable maintenance in E. coli cells, replicated in the presence of chloramphenicol and though unable to synthesize colicin, confered upon cells resistance to colicin K. The mode of ColK DNA replication is studied in mutants temperature-sensitive for the replication of chromosomal DNA. ColK DNA replication is shown to be virtually independent of the dnaA gene product and only slightly dependent on that of the dnaC gene. No replication occurs in the dnaB, dnaF and dnaG mutants at non-permissive temperature.
对来自产K和X大肠杆菌素的大肠杆菌K235细胞的一部分质粒DNA进行了研究。已表明该菌株的细胞含有四种分子量分别为21.6×10⁶、38.8×10⁶道尔顿的质粒。用总质粒DNA转化大肠杆菌C600产生了含有单个质粒——产大肠杆菌素K因子（ColK，分子量4.4×10⁶）的克隆。ColK DNA在细胞中以大量拷贝存在，在氯霉素存在下复制，需要DNA聚合酶I。用EcoRI酶处理ColK DNA时会形成分子量分别为3.4×10⁶和1.1×10⁶的两个片段。使用噬菌体T4 DNA连接酶环化后，3.4×10⁶片段能够在大肠杆菌细胞中自主复制并稳定维持，在氯霉素存在下复制，虽然不能合成大肠杆菌素，但赋予细胞对大肠杆菌素K的抗性。在对染色体DNA复制温度敏感的突变体中研究了ColK DNA的复制模式。结果表明，ColK DNA的复制实际上不依赖于dnaA基因产物，仅略微依赖于dnaC基因产物。在非允许温度下，dnaB、dnaF和dnaG突变体中不发生复制。
