Two essential replicative DNA polymerases exchange dynamically during DNA replication and after replication fork arrest

The replisome is the multi-protein complex responsible for faithful replication of chromosomal DNA. Using single-molecule super-resolution imaging, we characterized the dynamics of three replisomal proteins in live Bacillus subtilis cells: the two replicative DNA polymerases, PolC and DnaE, and a processivity clamp loader subunit, DnaX. We quantified the protein mobility and dwell times during normal replication and following both damage-independent and damage-dependent replication fork stress. With these results, we report the dynamic and cooperative process of DNA replication based on changes in the measured diffusion coefficients and dwell times. These experiments show that the replisomal proteins are all highly dynamic and that the exchange rate depends on whether DNA synthesis is active or arrested. Our results also suggest coupling between PolC and DnaX in the DNA replication process, and indicate that DnaX provides an important role in synthesis during repair. Furthermore, our results show that DnaE provides a limited contribution to chromosomal replication and repair.