Initiation of DNA replication in Escherichia coli. III. Genetic analysis of the dna mutant exhibiting rifampicin-sensitive resumption of replication.

Temperature-sensitive mutants defective in the initiation of DNA replication are exposed to a non-permissive temperature to complete already initiated replication, and are transferred back to a permissive temperature. DNA synthesis can resume in the presence of rifampicin or rifampicin plus chloramphenicol in strain PC2 (dnaC2), but not in strain N167 (dna-167). In the presence of chloramphenicol alone, however, DNA synthesis can resume in both strains (Hirage and Saito, 1973, 1974). The double mutants carrying the dna-167 and dnaC2 mutations show the rifampicin-sensitive resumption of DNA replication as the dna-167 mutant. The rifampicin-sensitive character (designated as Rrr-) is closely linked with the temperature sensitivity of the dna-167 mutant in P1 transduction. The gene order is dna-167-tna-phoS-uncA-ilv. The Rrr- character does not correlate with the inactivation of the altered product of the mutated dna-167 gene at various temperatures in the double mutant carrying dna-167 and dnaC2. Although dnaC2 strains show the Rrr+ phenotype, the dnaC2 strains received the ilv-dnaA region of the Ts+ revertants obtained from a dna-167 strain show the Rrr- phenotype. These results suggest that the dna-167 mutant has two mutations which are closely linked to each other, controlling the Rrr- phenotype and the temperature sensitivity, respectively.