Redox-driven ADAR1 activation promotes Okazaki fragment maturation and DNA replication integrity.

Okazaki fragment maturation requires efficient removal of RNA primers to form a continuous lagging strand, yet how mismatched primers introduced by error-prone primase are corrected remains unresolved. Here, we show that physiological levels of reactive oxygen species (ROS) initiate a redox-dependent mechanism that drives ADAR1-mediated adenosine-to-inosine (A-to-I) editing. Oxidation triggers ADAR1 dimerization at replication forks, enhancing RNA editing of mismatched primers-particularly those caused by ATP misincorporation on d(T+C)-rich centromeric DNA. This A-to-I editing step facilitates more efficient RNA primer degradation by RNase H2, thereby ensuring proper Okazaki fragment maturation. Disruption of ADAR1 oxidation results in increased unligated Okazaki fragments, single-stranded gaps and double-strand breaks, most prominently at centromeres. These findings reveal a role for ROS in safeguarding lagging-strand synthesis by coupling ADAR1 oxidation-induced A-to-I RNA editing to replication fork stability.