Aberrant double-strand break repair in rad51 mutants of Saccharomyces cerevisiae

A number of studies of Saccharomyces cerevisiae have revealed RAD51-indepen dent recombination events. These include spontaneous and double-strand brea k-induced recombination between repeated sequences, and capture of a chromo some arm by break-induced replication. Although recombination between inver ted repeats is considered to be a conservative intramolecular event, the la ck of requirement for RAD51 suggests that repair can also occur by a noncon servative mechanism. We propose a model for RAD51-independent recombination by one ended strand invasion coupled to DNA synthesis, followed by single- strand annealing. The Rad1/Rad10 endonuclease is required to trim intermedi ates formed during single-strand annealing and thus was expected to be requ ired for RAD51-independent events by this model. Double-strand break repair between plasmid-borne inverted repeats was less efficient in rad1 rad51 do uble mutants than in rad1 and rad51 strains. In addition, repair events wer e delayed and frequently associated with plasmid loss. Furthermore, the rep air products recovered from the rad1 rad51 strain were primarily in the cro ssover configuration, inconsistent with conservative models for mitotic dou ble-strand break repair.