RECQ4 arginine methylation suppresses single-stranded DNA gap accumulation at replication forks.

The role of protein arginine methylation in regulating transcription and RNA processing is well established, but its function in DNA replication remains poorly understood. In this study, we identify asymmetric dimethylarginine (aDMA) modification of the RECQ4 helicase as a key mechanism linking arginine methylation to replication control. Five arginine residues located within a glycine/arginine-rich region adjacent to the helicase domain of RECQ4 are targeted by type I PRMTs. This modification is enriched during S phase and promotes nuclear localization of RECQ4. On chromatin, aDMA modification is not required for replication origin firing but instead stabilizes the association of DNA polymerase δ with the MCM2-7 replicative helicase complex, thereby ensuring faithful replication fork progression. Mutation of the aDMA-modified residues (the 5RK mutant) leads to aberrant replication complexes and accumulation of single-stranded DNA gaps, resulting in slowed replication fork progression. These defects trigger G2/M arrest and increased anaphase bridge formation, consistent with incomplete DNA replication. Furthermore, cells expressing the 5RK mutant exhibit reduced sensitivity to the PRMT inhibitor MS023, highlighting disruption of RECQ4 methylation-mediated genome stability as a key mechanism underlying MS023-induced cytotoxicity.