Bloom helicase mediates formation of large single–stranded DNA loops during DNA end processing

Chaoyou Xue, Sameer J. Salunkhe, Nozomi Tomimatsu, Ajinkya S. Kawale, Youngho Kwon, Sandeep Burma, Patrick Sung () and Eric C. Greene ()
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Chaoyou Xue: Columbia University
Sameer J. Salunkhe: University of Texas Health Science Center at San Antonio
Nozomi Tomimatsu: Chinese Academy of Sciences
Ajinkya S. Kawale: University of Texas Health Science Center at San Antonio
Youngho Kwon: University of Texas Health Science Center at San Antonio
Sandeep Burma: University of Texas Health Science Center at San Antonio
Patrick Sung: University of Texas Health Science Center at San Antonio
Eric C. Greene: Columbia University

Nature Communications, 2022, vol. 13, issue 1, 1-16

Abstract: Abstract Bloom syndrome (BS) is associated with a profoundly increased cancer risk and is caused by mutations in the Bloom helicase (BLM). BLM is involved in the nucleolytic processing of the ends of DNA double–strand breaks (DSBs), to yield long 3′ ssDNA tails that serve as the substrate for break repair by homologous recombination (HR). Here, we use single–molecule imaging to demonstrate that BLM mediates formation of large ssDNA loops during DNA end processing. A BLM mutant lacking the N–terminal domain (NTD) retains vigorous in vitro end processing activity but fails to generate ssDNA loops. This same mutant supports DSB end processing in cells, however, these cells do not form RAD51 DNA repair foci and the processed DSBs are channeled into synthesis–dependent strand annealing (SSA) instead of HR–mediated repair, consistent with a defect in RAD51 filament formation. Together, our results provide insights into BLM functions during homologous recombination.

Date: 2022
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DOI: 10.1038/s41467-022-29937-7

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