Host: The Japan Radiation Research Society
Post-replication DNA repair facilitates resumption of DNA synthesis following replication fork stalling at sites of DNA damage. Despite the importance of RAD18 and polymerase h for post-replication repair, the molecular mechanisms by which these factors are recruited to stalled replication forks are not well understood. In this report, we present evidences that human RAD18 protein preferentially binds to forked DNA structures and that RAD18 and replication protein A bind long single-stranded DNA in a cooperative manner, which are known to be localized at stalled replication forks. The SAP domain of RAD18 is crucial for RAD18 binding to the DNA substrates. RAD18 mutated in the SAP domain fails to accumulate at sites of DNA damage in vivo, and does not guide DNA polymerase h to stalled replication forks. The SAP-domain mutant fails to suppress the UV-sensitivity of Rad18-knockout cells. Furthermore, RAD18 is required for guiding polymerase h (and also polymerase _) to stalled replication sites. These results suggest that RAD18 is recruited to stalled replication forks via interactions with forked DNA or long single-stranded DNA structure, which are required for initiating post-replication repair.
