Double-strand breaks at an initiation site for meiotic gene conversion

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Abstract
IT has been proposed that the initiation of meiotic recombination involves either single-strand or double-strand breaks in DNA1–3. It is difficult to distinguish between these on the basis of genetic evidence because they give rise to similar predictions4–6. All models invoke initiation at specific sites to explain polarity, which is a gradient in gene conversion frequency from one end of a gene to the other. In the accompanying paper7 we describe the localization of an initiation site for gene conversion to the promoter region of the ARG4 gene of the yeast Saccharomyces cerevisiae. Here, we show that a double-strand break appears at the ARG4 recombination initiation site at the time of recombination, and that the broken DNA molecules end in long single-stranded tails.