Removal of nonhomologous DNA ends in double-strand break recombination: the role of the yeast ultraviolet repair gene RAD1.

Double-strand breaks (DSBs) in Saccharomyces cerevisiae can be repaired by gene conversions or by deletions resulting from single-strand annealing between direct repeats of homologous sequences. Although rad1 mutants are resistant to x-rays and can complete DSB-mediated mating-type switching, they could not complete recombination when the ends of the break contained approximately 60 base pairs of nonhomology. Recombination was restored when the ends of the break were made homologous to donor sequences. Additionally, the absence of RAD1 led to the frequent appearance of a previously unobserved type of recombination product. These data suggest RAD1 is required to remove nonhomologous DNA from the 3' ends of recombining DNA, a process analogous to the excision of photodimers during repair of ultraviolet-damaged DNA.