Smarcal1-Mediated Fork Reversal Triggers Mre11-Dependent Degradation of Nascent DNA in the Absence of Brca2 and Stable Rad51 Nucleofilaments.

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Kolinjivadi, Arun Mouli 
Sannino, Vincenzo 
De Antoni, Anna 
Zadorozhny, Karina 

Brca2 deficiency causes Mre11-dependent degradation of nascent DNA at stalled forks, leading to cell lethality. To understand the molecular mechanisms underlying this process, we isolated Xenopus laevis Brca2. We demonstrated that Brca2 protein prevents single-stranded DNA gap accumulation at replication fork junctions and behind them by promoting Rad51 binding to replicating DNA. Without Brca2, forks with persistent gaps are converted by Smarcal1 into reversed forks, triggering extensive Mre11-dependent nascent DNA degradation. Stable Rad51 nucleofilaments, but not RPA or Rad51T131P mutant proteins, directly prevent Mre11-dependent DNA degradation. Mre11 inhibition instead promotes reversed fork accumulation in the absence of Brca2. Rad51 directly interacts with the Pol α N-terminal domain, promoting Pol α and δ binding to stalled replication forks. This interaction likely promotes replication fork restart and gap avoidance. These results indicate that Brca2 and Rad51 prevent formation of abnormal DNA replication intermediates, whose processing by Smarcal1 and Mre11 predisposes to genome instability.

Brca2, DNA replication, Mre11, Rad51, Xenopus laevis, fork protection, Animals, BRCA2 Protein, Binding Sites, DNA, DNA Helicases, DNA Polymerase I, DNA Polymerase III, DNA Replication, DNA-Binding Proteins, Endodeoxyribonucleases, Exodeoxyribonucleases, Female, Genomic Instability, Humans, MRE11 Homologue Protein, Male, Mutation, Protein Binding, Rad51 Recombinase, Replication Origin, Saccharomyces cerevisiae Proteins, Time Factors, Xenopus Proteins, Xenopus laevis
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Mol Cell
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Wellcome Trust (104641/Z/14/Z)
This work was funded by the Associazione Italiana per Ricerca sul Cancro (AIRC), European Research Council (ERC) Consolidator Grant 614541, the Armenise-Harvard Foundation career development award, Epigen Progetto Bandiera (4.7), AICR-Worldwide Cancer Research (13-0026), and Fondazione Telethon Grant GGP13-071 (to V.C.); by Wellcome Trust Investigator Award 104641/Z/14/Z (to L.P.); by the Czech Science Foundation (GACR 17-17720S and 13-26629S) and Project LQ1605 from the National Program of Sustainability II (MEYS CR) (to L.K.); and by NIH grant R01CA197774 and Susan G. Komen CCR grant CCR16377030 (to A.C.). V.S. is funded by a Fondazione Veronesi (FUV) personal postdoctoral fellowship.