A unique arginine cluster in PolDIP2 enhances nucleotide binding and DNA synthesis by PrimPol

Replication forks often stall at damaged DNA. Resumption of DNA synthesis can occur by replacement of the replicative DNA polymerase with specialized, error-prone translesion DNA polymerases (TLS), that have higher tolerance for damaged substrates. Several of these polymerases (Pol{lambda}, Pol{eta} and PrimPol) are stimulated in DNA synthesis through interaction with PolDIP2, however the mechanism of this PolDIP2-dependent stimulation is still unclear. Here we show that PrimPol uses a flexible loop to interact with the C-terminal ApaG-like domain of PolDIP2, and that this contact is essential for PrimPols enhanced processivity. PolDIP2 increases PrimPols primer-template and dNTP binding affinity, which concomitantly enhances PrimPols nucleotide incorporation efficiency. This activity is dependent on a unique arginine cluster in PolDIP2 and could be essential for PrimPol to function in vivo, since the polymerase activity of PrimPol alone is very limited. This mechanism, where the affinity for dNTPs gets increased by PolDIP2 binding, could be common to all other PolDIP2-interacting TLS polymerases, i.e. Pol{lambda}, Pol{eta}, Pol{zeta} and REV1, and might be critical for their in vivo function of tolerating DNA lesions at physiological nucleotide concentrations.