Visualizing bacterial DNA replication and repair with molecular resolution.

Although DNA replication and repair in bacteria have been extensively studied for many decades, in recent years the development of single-molecule microscopy has provided a new perspective on these fundamental processes. Because single-molecule imaging super-resolves the nanometer-scale dynamics of molecules, and because single-molecule imaging is sensitive to heterogeneities within a sample, this nanoscopic microscopy technique measures the motions, localizations, and interactions of proteins in real time without averaging ensemble observations, both in vitro and in vivo. In this Review, we provide an overview of several recent single-molecule fluorescence microscopy studies on DNA replication and repair. These experiments have shown that, in both Escherichia coli and Bacillus subtilis the DNA replication proteins are highly dynamic. In particular, even highly processive replicative DNA polymerases exchange to and from the replication fork on the scale of a few seconds. Furthermore, single-molecule investigations of the DNA mismatch repair (MMR) pathway have measured the complex interactions between MMR proteins, replication proteins, and DNA. Single-molecule imaging will continue to improve our understanding of fundamental processes in bacteria including DNA replication and repair.