A temperature-sensitive Escherichia coli mutant defective in DNA replication: dnaN, a new gene adjacent to the dnaA gene.

Abstract

An Escherichia coli mutant defective in replication of the chromosome has been isolated from temperature-sensitive mutants that cannot support colicin E1 plasmid DNA synthesis in the presence of chloramphenicol. Cellular DNA synthesis of the mutant ceases almost immediately after transfer to the nonpermissive temperature. The defect is due to a single mutation, dna-59, which is located close to the sites of dnaA mutations and a couR mutation conferring DNA gyrase with resistance to coumermycin. The dna-59 mutant is not able to support DNA synthesis of λ phage at the high temperature. The mutant also restricts growth of ϕX174 phage at the high temperature, but permits formation of supercoiled closedcircular duplex replicative intermediates. T7 phage can grow on the mutant even at the high temperature.