THE LOCATION AND STRUCTURE OF DOUBLE-STRAND DNA BREAKS INDUCED DURING YEAST MEIOSIS - EVIDENCE FOR A COVALENTLY-LINKED DNA-PROTEIN INTERMEDIATE

We have determined the precise location and structure of the double-strand DNA breaks (DSBs) formed during Saccharomyces cerevisiae meiosis. Breaks were examined at two recombination hot spots in both wildtype and rad50S mutant cells. At both loci, breaks occurred at multiple, irregularly spaced sites in a similar to 150 nucleotide interval contained within an area of nuclease-hypersensitive chromatin. No consensus sequence could be discerned at or around break sites. Patterns of cleavage observed on individual strands indicated that breaks initially form with a two nucleotide 5' overhang. Broken strands from rad50S mutant cells contained tightly bound protein at their 5' ends. We suggest that, in S.cerevisiae, meiotic recombination is initiated by a DSB-forming activity that creates a covalently linked protein-DNA intermediate.