Recombination factors at replication forks : restart or protect ?

Orateur : Sarah LAMBERT (Institut Curie, Paris)

The alteration of replication forks progression induces replication stress and mitotic abnormalities, two main features of cancer cells ; yet how stressed forks impair balanced chromosome segregation remains poorly defined. To avoid the persistence of un-replicated parental DNA by mitosis, stressed forks are rescued by opposite forks or restarted through DNA repair pathways such as Homologous Recombination. Here, we followed in vivo the fate of a single polar fork arrest in fission yeast. We report that a single terminally arrested fork, with no apparent un-replicated parental DNA, is converted into an anaphase bridge. We demonstrate that Rad52/Rad51 mediated-fork protection is critical to avoid pathological collision of an ongoing fork progressing towards a blocked fork. Unrestrained Exo1 activity results in up to 3Kb large ssDNA gaps upstream arrested forks, which are responsible for mitotic sister chromatid bridging, chromosome breakage, mutations and cell death. Using a separation-of-function rad51 mutant, we establish that Rad51 binding is sufficient to safeguard terminally arrested forks and avoid mitotic sister chromatid non-disjunction. Our data enlighten the importance of Rad51-mediated fork-protection in replication dynamics : this function is critical to safely rescue arrested forks though the progression of opposite forks.

Télécharger dans mon agenda