Replication protein A (RPA) sumoylation positively influences the DNA damage checkpoint response in yeast

The DNA damage response relies on protein modifications to elicit physiological changes required for coping with genotoxic conditions. Besides canonical DNA damage checkpoint-mediated phosphorylation, DNA damage-induced sumoylation has recently been shown to promote genotoxin survival. Cross-talk between these two pathways exists in both yeast and human cells. In particular, sumoylation is required for optimal checkpoint function, but the underlying mechanisms are not well-understood. To address this question, we examined the sumoylation of the first responder to DNA lesions, the ssDNA-binding protein complex replication protein A (RPA) in budding yeast (Saccharomyces cerevisiae). We delineated the sumoylation sites of the RPA large subunit, Rfa1 on the basis of previous and new mapping data. Findings using a sumoylation-defective Rfa1 mutant suggested that Rfa1 sumoylation acts in parallel with the 9-1-1 checkpoint complex to enhance the DNA damage checkpoint response. Mechanistically, sumoylated Rfa1 fostered an interaction with a checkpoint adaptor protein, Sgs1, and contributed to checkpoint kinase activation. Our results suggest that SUMO-based modulation of a DNA damage sensor positively influences the checkpoint response.