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Publication Abstract from PubMed

DNA double-strand breaks (DSBs) present a critical threat to genomic integrity, often precipitating genomic instability and oncogenesis. Repair of DSBs predominantly occurs through homologous recombination (HR) and non-homologous end joining (NHEJ). In HR-deficient cells, DNA polymerase theta (Poltheta) becomes critical for DSB repair via microhomology-mediated end joining (MMEJ), also termed theta-mediated end joining (TMEJ). Thus, Poltheta is synthetically lethal with BRCA1/2 and other HR factors, underscoring its potential as a therapeutic target in HR-deficient cancers. However, the molecular mechanisms governing Poltheta-mediated MMEJ remain poorly understood. Here we present a series of cryo-electron microscopy structures of the Poltheta helicase domain (Poltheta-hel) in complex with DNA containing different 3'-ssDNA overhangs. The structures reveal the sequential conformations adopted by Poltheta-hel during the critical phases of DNA binding, microhomology searching, and microhomology annealing. The stepwise conformational changes within the Poltheta-hel subdomains and its functional dimeric state are pivotal for aligning the 3'-ssDNA overhangs, facilitating the microhomology search and subsequent annealing necessary for DSB repair via MMEJ. Our findings illustrate the essential molecular switches within Poltheta-hel that orchestrate the MMEJ process in DSB repair, laying the groundwork for the development of targeted therapies against the Poltheta-hel.

Structural basis for Poltheta-helicase DNA binding and microhomology-mediated end-joining.,Ito F, Li Z, Minakhin L, Khant HA, Pomerantz RT, Chen XS Nat Commun. 2025 Apr 19;16(1):3725. doi: 10.1038/s41467-025-58441-x. PMID:40253368^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.