FIGURE 5: DSB repair by NHEJ and HR. The conserved mechanisms of DSB repair by NHEJ and HR are illustrated with budding yeast proteins. Left; Ku encircles DSB ends, recruiting the Lif1-Dnl4 and Nej1 ligase complex to promote NHEJ. Right; Stimulated by phosphorylated Sae2, Mre11 introduces nicks in the 5ʹ-terminated DNA strands, destabilizing Ku. At the nicks, Exo1 and Sgs1-Dna2 initiate long-range end-resection, exposing ssDNA, which is first coated by RPA, then by recombinase Rad51. The Rad51 nucleoprotein filament seeks out and invades a homologous donor sequence to initiate DNA repair synthesis. HR leads mostly to non-crossover products with a repair patch where new DNA has been synthesized.