Point Mutations V546E and D547H of the RBM-B Motif Do Not Affect the Binding of PrimPol to RPA and DNA

The human primase-polymerase PrimPol is a key participant of the mechanism of DNA synthesis restart during replication fork stalling at sites of DNA damage. PrimPol has DNA primase activity and synthesizes DNA primers that are used by processive DNA polymerases to continue replication. Recruitment of PrimPol to the sites of DNA damage, as well as stimulation of catalytic activity, depends on interaction with the replicative protein RPA, which binds single-stranded DNA. The C-terminal domain of PrimPol contains a negatively charged RPA-binding motif (RBM), mutations in which disrupt the interaction between two proteins. The RBM motif also plays a role in the negative regulation of PrimPol interaction with DNA. Deletion of the RBM dramatically increases PrimPol affinity to DNA and stimulates PrimPol activity. The mechanism of RBM-mediated regulation of PrimPol activity is unclear. The relatively strong negative charge of RBM potentially may contribute to the interaction of PrimPol with RPA and DNA. RBM contains two negatively charged regions RBM-A and RBM-B. In this work, we additionally added (substitution V546E) or decreased (substitution D547H) a negative charge in RBM-B PrimPol and characterized these mutant variants biochemically. It was shown that the local change in the RBM-B charge has no effect on the interaction of PrimPol with DNA and RPA, or of the catalytic activity of the enzyme.