 Two primary models for how homologous recombination repairs double @-@ strand breaks in DNA are the double @-@ strand break repair ( DSBR ) pathway ( sometimes called the double Holliday junction model ) and the synthesis @-@ dependent strand annealing ( SDSA ) pathway . The two pathways are similar in their first several steps . After a double @-@ strand break occurs , the MRX complex ( MRN complex in humans ) binds to DNA on either side of the break . Next a resection , in which DNA around the 5 ' ends of the break is cut back , is carried out in two distinct steps . In the first step of resection , the MRX complex recruits the Sae2 protein . The two proteins then trim back the 5 ' ends on either side of the break to create short 3 ' overhangs of single @-@ strand DNA . In the second step , 5 ' → 3 ' resection is continued by the Sgs1 helicase and the <unk> and <unk> nucleases . As a helicase , Sgs1 " <unk> " the double @-@ strand DNA , while <unk> and <unk> 's nuclease activity allows them to cut the single @-@ stranded DNA produced by Sgs1 . 
