Professor Liaw Hung-jiun’s Laboratory

Nucleostemin promotes RAD51 filament assembly on double-stranded DNA to protect stalled replication forks

During DNA replication, cells may encounter DNA lesions or other obstacles that slow or stall replication fork progression, a phenomenon known as replication stress. Prolonged replication fork stalling can lead to DNA double-strand breaks (DSBs) and genome instability. To prevent such deleterious consequences, cells can remodel stalled replication forks into a more stable structure known as a reversed fork. However, additional protective mechanisms are required to prevent the newly synthesized DNA from being degraded by nucleases such as MRE11.

In this study, conducted in collaboration with Professor Peter Chi of the Institute of Biochemical Sciences and Professor Hung-Wen Li of the Department of Chemistry at National Taiwan University, with Ph.D. students Siang-Sheng Tsai (co-first author) and Chia-Tai Hung contributing to the research, we identified Nucleostemin (NS) as a critical factor in protecting stalled replication forks. Upon induction of replication stress, NS accumulates at stalled replication forks. Depletion of NS markedly increases MRE11-mediated degradation of newly synthesized DNA, whereas inhibition of MRE11 partially restores this phenotype, demonstrating that NS plays an essential role in replication fork protection.

Further investigation revealed that NS can directly bind to DNA and physically interact with the DNA repair protein RAD51, thereby facilitating the recruitment and accumulation of RAD51 at stalled replication forks. Single-molecule analyses further demonstrated that NS promotes the formation of a protective RAD51–DNA structure on double-stranded DNA. Together, NS and RAD51 protect nascent DNA from degradation by MRE11.

Our findings uncover a previously unrecognized mechanism by which NS cooperates with RAD51 to protect stalled replication forks, providing new insights into how cells preserve DNA integrity and maintain genome stability under replication stress.

Chih-Chun Chang^†, Siang-Sheng Tsai^† (蔡翔勝), Chang-Le Chou, Yi-Hsuan Chang, Chia-Tai Hung (洪加泰), Robert YL Tsai, Hung-Wen Li^*, Hungjiun Liaw^* (廖泓鈞), Peter Chi^* (2026) Nucleostemin promotes RAD51 filament assembly on double-stranded DNA to protect stalled replication forks. Nucleic Acids Research 54 (15), gkag773. https://pubmed.ncbi.nlm.nih.gov/42573072/ (^†Joint first authors; ^*Corresponding authors).