Single-molecule tracking of RNA-DNA hybrid removal enzymes important for lagging-strand replication.

The formation of RNA-DNA hybrid (RDH) primers by primase is an essential step in the recruitment of DNA polymerase during replication initiation and for the synthesis of each Okazaki fragment on the lagging strand. In addition to primers, RDHs form through misincorporation of ribonucleotides by DNA polymerase during elongation and by formation of R-loops during transcription. R-loops are three-stranded structures that form when the nascent mRNA anneals to the template DNA strand, displacing the complementary DNA strand. The persistence of RDHs is deleterious to genome stability in all cells because they increase susceptibility to mutations, impaired replication fork progression, DNA double-stranded breaks, and genomic rearrangements. In many bacteria, it is well established that components of the replicative DNA polymerase form a macromolecular complex that can be imaged using single-molecule or ensemble fluorescence approaches. The spatiotemporal regulation of proteins involved in RDH removal during lagging-strand maturation is less clear. Here, we study three proteins that are involved in the removal of RDHs from the lagging strand during DNA replication in the Gram-positive bacterium