Dynamic suppression of Holliday junction resolution enables meiotic crossover patterning. Saccharomyces cerevisiae strain:S96xYJM hybrid

Meiotic crossing-over derives from the resolution of double-Holliday junctions (dHJs) by the MutLγ complex, Mlh1-Mlh3, and by three structure-specific endonucleases (SSEs): Mus81-Mms4(EME1), Yen1(GEN1) and Slx1-Slx4(BTB12)1-4. While SSEs contribute to dHJ processing, MutLγ has the unique ability to resolve dHJs at crossover (CO)-designated sites, which are spatially patterned along chromosomes3, 5. How and why cells implement pathway usage is unknown, but it has been proposed that chromosomal context plays an important role in specifying MutLγ function6. Here, we show that CDK-mediated phosphorylation of Yen1 inhibits its nuclease activity and precludes its recruitment to dHJs during prophase I. Yen1 mutants refractory to inhibitory phosphorylation resolve dHJs at CO-designated sites and, moreover, restore CO formation in cells lacking MutLγ. Unexpectedly, unrestrained Yen1 function leads to a defective spatial distribution of CO events, suggesting that temporal control of dHJ processing may be necessary for appropriate spacing of CO precursors along chromosomes. We propose that active suppression of Yen1 function, and by inference also Mus81-Mms4 and Slx1-Slx4, is a fundamental determinant in avoiding pathway competition and an important requirement for appropriate patterning of meiotic COs.