DNA replication fork rescue: A journey to the nuclear periphery

My lab has a long-standing interest in understanding the mechanism of recombination-dependent replication, a non-canonical DNA synthesis pathway that contributes to DNA replication completion at the cost of increased genome instability (1). RDR is initiated from arrested replication forks by the recombinase Rad51 and extended by DNA polymerase delta to ensure the restart of DNA synthesis (2). Recently, we discovered that the subsequent steps of RDR are spatially segregated in the nuclear space, based on local modifications by SUMO (3). Rad51-dependent fork remodeling and strand invasion occurs in the nucleoplasm while priming DNA synthesis requires relocation of arrested forks to nuclear pores complexes that are macromolecules embedded in the nuclear envelop to ensure molecular transport. We identified two distinct mechanisms by which the NPC environment ensures optimal RDR, both controlled by different NPC components (4, 5). I will discuss results from spatially resolved proteomics to decipher the atlas of factors associated with restarted forks in the fission yeast S. pombe.

1. Ait Saada A. et al. Unprotected Replication Forks Are Converted into Mitotic Sister Chromatid Bridges. Mol cell 2017. doi: 10.1016/j.molcel.2017.04.002.

2. Carr A. & Lambert S. Recombination-dependent replication: new perspectives from site-specific fork barriers.  Curr Opin Genet Dev. 2021. doi: 10.1016/j.gde.2021.07.008.

3. Kramarz K. et al. The nuclear pore primes recombination-dependent DNA synthesis at arrested forks by promoting SUMO removal.  Nat Commun. 2020. doi: 10.1038/s41467-020-19516-z.

4. Schirmeisen K. et al. SUMO protease and proteasome recruitment at the nuclear periphery differently affect replication dynamics at arrested forks. Nucleic Acids Res. 2024. doi: 10.1093/nar/gkae526.

5. Chakraborty S. et al. The fission yeast SUMO-targeted ubiquitin ligase Slx8 functionally associates with clustered centromeres and the silent mating-type region at the nuclear periphery.  Biol Open. 2024 doi: 10.1242/bio.061746.