FIGURE 1: Models for homology-dependent DSB repair.

(A) HR-mediated repair of a DSB is initiated by 5’ to 3’ resection of the DNA ends by the MRX complex and Sae2, and this resection is inhibited by the Ku complex. More extensive resection is then carried out by either Exo1 or the combined activities of the Sgs1-Top3-Rmi1 complex and Dna2. The resulting single-stranded DNA recruits the ssDNA-binding protein RPA. Rad52 mediates the loading of Rad51 onto RPA-coated ssDNA to form Rad51 nucleoprotein filaments capable of performing strand invasion. Repair can then proceed via the classical double-strand break repair model or the synthesis-dependent strand annealing model.

(B) One-ended breaks can be repaired by BIR, which can be Rad51-dependent (as shown here) or Rad51-independent. In BIR, strand invasion leads to the formation of a D-loop that migrates along the chromosome as the invading 3’ overhang is extended. The complementary strand is synthesized by conservative replication. For simplicity, not all proteins involved in DSB repair are shown.