Role of Polo-Kinase Cdc5 in DSB processing and repair in Saccharomyces cerevisiae

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 and deregulation of their activity has been linked to genomic rearrangements in both yeast and human cells (Iliaki et al., 2021; Rawal et al., 2016). In this study we found that loss of yeast Cdc5 kinase activity by hypomorphic mutation (Rawal et al., 2016) suppresses Rad51-dependent Break-Induced Replication (BIR) of a single DSB, but not Rad51-independent Single-Strand Annealing (SSA). Loss of Cdc5 kinase activity leads to reduced levels of Rad51 by ChIP at the donor locus and inefficient D-loop formation by a primer-extension assay during BIR repair, mimicking the absence of Rad55, a Rad51 paralog involved in proper assembling of the recombinogenic ssDNA filament. We also found that deletion of Srs2 helicase and translocase suppresses D-loop defect in BIR of both rad55 and cdc5 mutants. On the other hand, both cdc5 mutation and Rad55 deletion ameliorate srs2Δ-induced toxicity during BIR (Elango et al., 2017), and reduced Cdc5 activity loses its impact on BIR efficiency when both Rad55 and Srs2 are absent. Basing on additional results showing physical interaction between Cdc5 and Rad55, we are currently working on a model where Cdc5 regulates the maturation of the presynaptic filament and invasion prior BIR repair. Our results in yeast suggest novel mechanism through which PLKs might control genotoxic recombination events, hallmarks of tumorigenesis