A TEST OF THE DOUBLE-STRAND BREAK REPAIR MODEL FOR MEIOTIC RECOMBINATION IN SACCHAROMYCES-CEREVISIAE

We tested predictions of the double-strand break repair (DSBR) model f or meiotic recombination by examining the segregation patterns of smal l palindromic insertions, which frequently escape mismatch repair when in heteroduplex DNA. The palindromes flanked a well characterized DSB site at the ARG4 locus. The ''canonical'' DSBR model, in which only 5 ' ends are degraded and resolution of the four-stranded intermediate i s by Holliday junction resolvase, predicts that hDNA will frequently o ccur on both participating chromatids in a single event. Tetrads refle cting this configuration of hDNA were rare. In addition, a class of te trads not predicted by the canonical DSBR model was identified. This c lass represented events that produced hDNA in a ''trans'' configuratio n, on opposite strands of the same duplex on the two sides of the DSB site. Whereas most classes of convertant tetrads had typical frequenci es of associated crossovers, tetrads with trans hDNA were parental for flanking markers. Modified versions of the DSBR model, including one that uses a topoisomerase to resolve the canonical DSBR intermediate, are supported by these data.