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Structural basis of gap-filling DNA synthesis in the nucleosome by DNA Polymerase β | Nature Communications Single-strand breaks (SSBs) are one of the most prevalent forms of DNA damage found in the chromatinized genome and are repaired by single-strand break repair (SSBR) or base excision repair (BER). DNA polymerase beta (Pol β) is the primary enzyme responsible for processing the 1-nt gap intermediate in chromatin during SSBR and BER. To date, the mechanism used by Pol β to process a 1-nt gap in the context of chromatin remains poorly understood. Here, we use biochemical assays and cryogenic electron microscopy (cryo-EM) to determine the kinetic and structural basis of gap-filling DNA synthesis in the nucleosome by Pol β. This work establishes that Pol β uses a global DNA sculpting mechanism for processing 1-nt gaps in the nucleosome during SSBR and BER, providing fundamental insight into DNA repair in chromatin. DNA polymerase beta (Pol β) is the primary enzyme responsible for processing 1-nt gaps in chromatin during DNA repair. Here, the authors determine the kinetic and structural basi https://doi.org/10.1038/s41467-025-57915-2