The importance of the mechanism of homologous recombination (HR) in DNA repair and in the maintenance of genome stability is illustrated by the various genetic diseases caused by HR deregulation. One of the key steps in HR is the formation of filaments of the recombinase protein Rad51 on the ends of broken DNA. These nucleoprotein structures have the property of carrying out the search and then the invasion of an intact homologous DNA sequence which allows DNA repair synthesis. In the laboratory, we use a eukaryotic cell model, the yeast Saccharomyces cerevisiae, to study this step of homologous recombination. In this organism, the formation of Rad51 filaments is ensured by the Rad52 protein, in association with the protein complexes of Rad51 paralogs, Rad55-Rad57 and SHU. Rad55-Rad57 and SHU are known to protect Rad51 filaments against their destabilization by the translocase protein Srs2. We have shown that this is also the case for Rad52 (Ma et al., Elife 2018; Ma et al., Cells 2021). This control of Rad51 filaments formation avoids the formation of non-productive structures which can lead to cell death (Esta et al., PloS Genet, 2013). We also obtained results strongly arguing that Rad55-Rad57 allows to block the recruitment of translational polymerases in order to promote the restart by homologous recombination of replication forks blocked by DNA lesions (bioRxiv 2021.05.27.44600). We now continue to describe the details of the regulation of Rad51 filaments and we wish to define the nature of the potential toxicity of Rad51 filaments.

• Structure of the association of Rad52 with Rad51 filaments (collaboration with Françoise Ochsenbein - I2BC, CEA / CNRS)
• Structure of the Rad55-Rad57 and SHU complexes in association with Rad51 filaments (collaboration with Raphaël Guerois - I2BC, CEA / CNRS)
• How do these proteins inhibit the displacement of Rad51 filaments by Srs2?
• What distinguishes a Rad51 filament normally involved in the HR process, protected from Srs2, from a toxic filament, substrate of this protein?
• What is the cause of the potential toxicity of Rad51 filaments in cells lacking Srs2 activity? We plan to isolate this type of filaments in vivo in order to determine the mechanisms they hinder (replication, repair of lesions, late stages of HR, etc.)

Yeast genetics

Molecular biology (ChIP, co-IP…)

Protein biochemistry (protein purification, in vitro analysis of nucleoprotein complexes)