Roles of Polo kinase Cdc5 in DNA double strand breaks processing and repair

Polo-Like Kinases (PLKs) are key regulators of cell cycle, promoting mitotic completion and cell proliferation from yeast to mammals, and their misregulation is a hallmark of several cancers. Importantly, PLKs have been shown to phosphorylate different DNA repair factors (1–3) and overexpression of Cdc5, only PLK in S.cerevisiae, was shown to slow down DSB resection at a HO break (4). In this study we found that loss of Cdc5 kinase activity by hypomorphic mutation (5) speeds up end resection in a Exo1 nuclease dependent fashion, and, consistently, hampers NHEJ repair. Moreover, our data suggest that Cdc5 activity is critical for both intra- and inter-chromosomal Break-Induced Replication, but not for Rad51-independent Single-Strand Annealing. Loss of Cdc5 kinase activity leads to reduced levels of Rad51 at the donor locus and inefficient D-loop formation during BIR repair. Deletion of Srs2 helicase and translocase, but not of Mph1 and Sgs1, suppresses D-loop defect of cdc5 mutant cells. On the other hand, reduced Cdc5 kinase activity ameliorates srs2D toxicity during recombination repair. We propose a model where Cdc5 is fundamental for early steps of DSB repair, controlling both the resection process and proper assembling of Rad51 onto ssDNA filament for recombination. 1. Matos, J., Blanco, M. G., Maslen, S., Skehel, J. M. & West, S. C. Regulatory Control of the Resolution of DNA Recombination Intermediates during Meiosis and Mitosis. Cell 147, 158–172 (2011). 2. Grigaitis, R. et al. Phosphorylation of the RecQ Helicase Sgs1/BLM Controls Its DNA Unwinding Activity during Meiosis and Mitosis. Developmental Cell 53, 706-723.e5 (2020). 3. Yata, K. et al. Plk1 and CK2 Act in Concert to Regulate Rad51 during DNA Double Strand Break Repair. Mol Cell 45, 371–383 (2012). 4. Donnianni, R. A. et al. Elevated Levels of the Polo Kinase Cdc5 Override the Mec1/ATR Checkpoint in Budding Yeast by Acting at Different Steps of the Signaling Pathway. PLoS Genet 6, e1000763 (2010). 5. Rawal, C. C. et al. Reduced kinase activity of polo kinase Cdc5 affects chromosome stability and DNA damage response in S. cerevisiae. Cell Cycle 15, 2906–2919 (2016).