The conversion gradient at HIS4 of Saccharomyces cerevisiae. II. A role for mismatch repair directed by biased resolution of the recombinational intermediate

Salient features of recombination at ARG4 of Saccharomyces provoke a variat ion of the double-strand-break repair (DSBR) model that has the following f eatures: (1) Holliday junction cutting is biased in favor of strands upon w hich DNA synthesis occurred during formation of the joint molecule (this bi as ensures that cutting both junctions of the joint-molecule intermediate a rising during DSBR usually leads to crossing over); (2) cutting only one ju nction gives noncrossovers; and (3) repair of mismatches that are semirefra ctory to mismatch repair and/or far from the DSB site is directed primarily by junction resolution. The bias in junction resolution favors restoration of 4:4 segregation when such mismatches and the directing junction are on the same side of the DSB site. Studies at HIS4 confirmed the predicted infl uence of the bias injunction resolution on the conversion gradient, type of mismatch repair, and frequency of aberrant 5:3 segregation, as well as the predicted relationship between mismatch repair and crossing over.