[Replication characteristics of colicinogenic plasmid ColK in Escherichia coli cells].

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.