Investigating the role of RAD51 phosphorylation during the cell cycle

Thesis

The RAD51 recombinase safeguards genomic integrity by promoting double-strand break repair and replication fork protection. PLK1-dependent RAD51 phosphorylation contributes to RAD51 recruitment at DNA double strand breaks and stalled replication forks. During an unperturbed cell cycle, RAD51 phosphorylation peaks in late G2 phase and mitosis, suggesting a role for (phosphorylated) RAD51 during the later stages of the cell cycle.

In this thesis, CRISPR/Cas9 RAD51 phospho-mutants were generated to assess the importance of RAD51 phosphorylation during the cell cycle. Consistent with previous research, I present data which suggest that RAD51 phosphorylation contributes to RAD51 recruitment at stressed DNA. I further demonstrate that RAD51 phosphorylation protects against the detrimental consequences of replication stress and that RAD51 phosphorylation may influence replication rate and mitotic duration in unperturbed conditions.

I present evidence for the role of RAD51 in mitotic DNA synthesis (MiDAS), as well as the contribution of RAD51 phosphorylation in this process. Based on the data presented here, I hypothesize that RAD51 phosphorylation enables the recruitment of RAD51 to mitotic chromatin to promote MiDAS. Break-dependent and break-independent mechanisms of MiDAS are proposed and the potential roles of RAD51 are discussed in each. The interplay between MiDAS and mitotic duration is explored. Anaphase onset is found to be delayed upon RAD51 inhibition, while polymerase inhibition decreases mitotic duration. A model is proposed in which the presence of mitotic DNA breaks and active replication intermediates in mitosis prevent SAC silencing, thereby ensuring enough time for the completion of replication prior to anaphase.

Authors: Wassing, I

• DOI: 10.5287/ora-zbd6opqbq
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English