SAW1 is required for SDSA double-strand break repair in S. cerevisiae

• Saw1 is required for Synthesis Dependent Strand Annealing in S. cerevisiae.
• Saw1 foci are temporally overlapped with Rad10 foci at SDSA sites.
• Few Saw1 foci appear at SDSA sites without Rad10.
• Temporal overlap of Saw1 and Rad10 foci at SDSA sites is not entirely coincident.

SAW1, coding for Saw1, is required for single-strand annealing (SSA) DNA double-strand break (DSB) repair in Saccharomycescerevisiae. Saw1 physically associates with Rad1 and Rad52 and recruits the Rad1–Rad10 endonuclease. Herein we show by fluorescence microscopy that SAW1 is similarly required for recruitment of Rad10 to sites of Synthesis-Dependent Strand Annealing (SDSA) and associates with sites of SDSA repair in a manner temporally overlapped with Rad10. The magnitude of induction of colocalized Saw1-CFP/Rad10-YFP/DSB-RFP foci in SDSA is more dramatic in S and G2 phase cells than in M phase, consistent with the known mechanism of SDSA. We observed a substantial fraction of foci in which Rad10 was localized to the repair site without Saw1, but few DSB sites that contained Saw1 without Rad10. Together these data are consistent with a model in which Saw1 recruits Rad1–Rad10 to SDSA sites, possibly even binding as a protein–protein complex, but departs the repair site in advance of Rad1–Rad10.