Rifampin-induced initiation of chromosome replication in dnaR-deficient Escherichia coli cells.

The dnaR130 mutant of Escherichia coli, which was thermosensitive in initiation of chromosome replication, was capable of thermoresistant DNA synthesis in the presence of rifampin at a low concentration that allowed almost normal RNA synthesis. The DNA synthesis in the presence of the drug depended on protein synthesis at the high temperature. The protein synthesis in the dnaR-deficient cells provided a potential for thermoresistant DNA synthesis to be induced at a high dose of the drug that almost completely prevented RNA synthesis. The induced synthesis was synchronously initiated from oriC and proceeded semiconservatively toward terC. The replication depended on the dnaA function, which was essential for normal initiation of replication from oriC. The capability for drug-induced replication was abolished by certain rifampin resistance mutations in the beta subunit of RNA polymerase. Thus, the drug can induce the dnaA-dependent initiation of replication in the dnaR-deficient cells through its effect on RNA polymerase. This result implies that the dnaR product is involved in the transcription obligatory for the initiation of replication of the bacterial chromosome.