RAD52-dependent and -independent homologous recombination initiated by Flp recombinase at a single FRT site flanked by direct repeats.

We have devised a system for isolating yeast DNA sequences that are able to act as initiators of recombination leading to deletions in mitotically growing yeast cells. This system has allowed us to identify the FRT site of the 2-micron site-specific recombinase Flp as such a sequence. We show that Flp is able to initiate recombination leading to deletions at a single FRT site in cir(o) strains. These results indicate that Flp is able to cleave a single FRT site, supporting the observation that the mechanism of cleavage by Flp is trans-horizontal. Interestingly, Flp can induce homologous recombination in both a RAD52-dependent and RAD52-independent manner. Our work provides a new system for the study of homologous recombination leading to deletions, in which the initiation step can be efficiently controlled. We discuss the possibility that Flp-induced, RAD52-independent events occur by single-strand annealing.