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bioRxiv · 10.1101/162677

The non-homologous end joining factor Ku orchestrates replication fork resection and fine-tunes Rad51-mediated fork restart

Teixeira-Silva, A.·Ait Saada, A.·Iraqui, I.·Nocente, M. C.·Freon, K.·Hardy, J.·Lambert, S.
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Abstract

Replication requires Homologous Recombination (HR) to stabilize and restart terminally-arrested forks. HR-mediated fork processing requires single stranded DNA (ssDNA) gaps and not necessarily Double Strand Breaks. We used genetic and molecular assays to investigate fork-resection and restart at dysfunctional, unbroken forks in Schizosaccharomyces pombe. We found that fork-resection is a two-step process coordinated by the non-homologous end joining factor Ku. An initial resection mediated by MRN/Ctp1 removes Ku from terminally-arrested forks, generating ~ 110 bp sized gaps obligatory for subsequent Exo1-mediated long-range resection and replication restart. The lack of Ku results in slower fork restart, excessive resection, and impaired RPA recruitment. We propose that terminally-arrested forks undergo fork reversal, providing a single DNA end for Ku binding which primes RPA-coated ssDNA. We uncover an unprecedented role for Ku in orchestrating resection of unbroken forks and in fine-tuning HR-mediated replication restart.\n\nO_LIKu orchestrates a two-steps DNA end-resection of terminally-arrested and unbroken forks\nC_LIO_LIMRN/Ctp1 removes Ku from terminally-arrested forks to initiate fork-resection\nC_LIO_LIa ~110 bp sized ssDNA gap is sufficient and necessary to promote fork restart.\nC_LIO_LIThe lack of Ku decreases ssDNA RPA-coating, and slows down replication fork restart.\nC_LI

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Teixeira-Silva, A., Ait Saada, A., Iraqui, I., Nocente, M. C., Freon, K., Hardy, J., Lambert, S.. 2017-07-12. The non-homologous end joining factor Ku orchestrates replication fork resection and fine-tunes Rad51-mediated fork restart. https://doi.org/10.1101/162677

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