The nucleolytic resolution of recombination intermediates in yeast mitotic cells.

In mitotic cells, the repair of double-strand breaks by Homologous Recombination (HR) is important for genome integrity. HR requires the orchestration of a subset of pathways for timely removal of joint-molecule intermediates that would otherwise prevent segregation of chromosomes in mitosis. The use of nucleases to resolve recombination intermediates is important for chromosome segregation, but is hazardous because crossovers can result in loss of heterozygosity (LOH) or chromosome rearrangements. Unregulated use of the nucleases involved in the resolution of recombination intermediates could also be a risk during replication. The yeast models ( Sacharomyces cerevisae and Schizosacharomyces pombe ) have proven effective in determining the major nucleases involved in the processing of such intermediates: Mus81-Mms4 and Yen1. Mus81-Mms4 and Yen1 are regulated by the cell cycle in a gradual activation during G2/M to keep the crossing-over risk low while ensuring proper removal of HJ intermediates.