Sae2p phosphorylation is crucial for cooperation with Mre11p for resection of DNA double-strand break ends during meiotic recombination in Saccharomyces cerevisiae.

Meiotic recombination is initiated by the introduction of DNA double-strand breaks (DSBs) at recombination hotspots. DSB ends are resected to yield ssDNA, which is used in a homology search. Sae2p, which is involved in the resection of DSB ends, is phosphorylated by the Mec1p and Tel1p kinases during meiosis. To clarify the role of Sae2p phosphorylation in meiotic recombination, three mutants with alanine substitutions (at two putative Mec1/Tel1 phosphorylation sites near the N terminus, at three sites near the C terminus or at all five sites) were constructed. Analysis of DSB ends during meiotic recombination demonstrated that phosphorylation of the three C-terminal phosphorylation sites is necessary for DSB end resection and that phosphorylation of the two N-terminal phosphorylation sites is required for the efficient initiation of DSB end resection. Sae2p was localized on meiotic chromosomes in the rad50S and mre11-H125R mutants, which accumulate DSB ends. Alanine substitutions of all phosphorylation sites did not affect localization of Sae2p on meiotic chromosomes. Although colocalization of Sae2p with Mre11p and recombinant formation were observed in the N-terminally mutated and the C-terminally mutated strains, these processes were drastically impaired in the quintuple mutant. These results indicate that phosphorylation of Sae2p is required to initiate resection and to improve the efficiency of resection through cooperation with the Mre11-Rad50-Xrs2 complex.