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The loading of RecA onto ssDNA by RecBCD is an essential step of RecBCD-mediated homologous recombination. RecBCD facilitates RecA-loading onto ssDNA in a χ-dependent manner via its RecB nuclease domain (RecBn). Before recognition of χ, RecBn is sequestered through interactions with RecBCD. It was proposed that upon χ-recognition, RecBn undocks, allowing RecBn to swing out via a contiguous 70 amino acid linker to reveal the RecA-loading surface, and then recruit and load RecA onto ssDNA. We tested this hypothesis by examining the interactions between RecBn (RecB928-1180) and truncated RecBCD (RecB1-927CD) lacking the nuclease domain. The reconstituted complex of RecB1-927CD and RecBn is functional in vitro and in vivo. Our results indicate that despite being covalently severed from RecB1-927CD, RecBn can still load RecA onto ssDNA, establishing that RecBn does not function while only remaining tethered to the RecBCD complex via the linker. Instead, RecBCD undergoes a χ-induced intramolecular rearrangement to reveal the RecA-loading surface. © The Author(s) 2024. Published by Oxford University Press on behalf of Nucleic Acids Research.


Theetha L Pavankumar, C Jason Wong, Yun Ka Wong, Maria Spies, Stephen C Kowalczykowski. Trans-complementation by the RecB nuclease domain of RecBCD enzyme reveals new insight into RecA loading upon χ recognition. Nucleic acids research. 2024 Mar 21;52(5):2578-2589

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PMID: 38261972

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