DNA polymerase (pol ) is a key player in DNA base excision repair (BER). Here, we describe the complex formation of pol with the protein arginine methyltransferase 1 (PRMT1). PRMT1 specifically methylated pol in vitro and in vivo. Arginine 137 was identified in pol as an important target for methylation by PRMT1. Neither the polymerase nor the dRP-lyase activities of pol were affected by PRMT1 methylation. However, this modification abolished the interaction of pol with proliferating cell nuclear antigen (PCNA). Together, our results provide evidence that PRMT1 methylation of pol might play a regulatory role in BER by preventing the involvement of pol in PCNA-dependent DNA metabolic events.--El-Andaloussi, N., Valovka, T., Toueille, M., Hassa, P. O., Gehrig, P., Covic, M., Hübscher, U., Hottiger, M. O. Methylation of DNA polymerase by protein arginine methyltransferase 1 regulates its binding to proliferating cell nuclear antigen.