A phenotype for enigmatic DNA polymerase II: a pivotal role for pol II in replication restart in UV-irradiated Escherichia coli.


DNA synthesis in Escherichia coli is inhibited transiently after UV irradiation. Induced replisome reactivation or "replication restart" occurs shortly thereafter, allowing cells to complete replication of damaged genomes. At the present time, the molecular mechanism underlying replication restart is not understood. DNA polymerase II (pol II), encoded by the dinA (polB) gene, is induced as part of the global SOS response to DNA damage. Here we show that pol II plays a pivotal role in resuming DNA replication in cells exposed to UV irradiation. There is a 50-min delay in replication restart in mutant cells lacking pol II. Although replication restart appears normal in DeltaumuDC strains containing pol II, the restart process is delayed for >90 min in cells lacking both pol II and UmuD'(2)C. Because of the presence of pol II, a transient replication-restart burst is observed in a "quick-stop" temperature-sensitive pol III mutant (dnaE486) at nonpermissive temperature. However, complete recovery of DNA synthesis requires the concerted action of both pol II and pol III. Our data demonstrate that pol II and UmuD'(2)C act in independent pathways of replication restart, thereby providing a phenotype for pol II in the repair of UV-damaged DNA.




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