Extensive 3′-overhanging, single-stranded DNA associated with the meiosis-specific double-strand breaks at the ARG4 recombination initiation site

Abstract

Meiosis-specific double-strand breaks occur at the initiation site for melotic gene conversion in the yeast ARG4 gene. Here we show that the break fragments end in extensive 3′-overhanging, single-stranded talls. The single-stranded talls vary in length, generating a gradlent of single-strandedness that parallels the gradient of gene conversion frequencies in ARG4. In strains carrying a rad50S mutation, which blocks meiotic recombination, the extensive single-stranded tails do not form, suggesting that their generation is an obligatory step in melotic recombination. Using the rad50S mutant, we have mapped the site of the ARG4 break to a small region within the genetically defined recombination initiation site. These results strongly support the double-strand break model of melotic recombination.