A role for Ddc1 in signaling meiotic double-strand breaks at the pachytene checkpoint.

The pachytene checkpoint prevents meiotic cell cycle progression in response to unrepaired recombination intermediates. We show that Ddc1 is required for the pachytene checkpoint in Saccharomyces cerevisiae. During meiotic prophase, Ddc1 localizes to chromosomes and becomes phosphorylated; these events depend on the formation and processing of double-strand breaks (DSBs). Ddc1 colocalizes with Rad51, a DSB-repair protein, indicating that Ddc1 associates with sites of DSB repair. The Rad24 checkpoint protein interacts with Ddc1 and with recombination proteins (Sae1, Sae2, Rad57, and Msh5) in the two-hybrid protein system, suggesting that Rad24 also functions at DSB sites. Ddc1 phosphorylation and localization depend on Rad24 and Mec3, consistent with the hypothesis that Rad24 loads the Ddc1/Mec3/Rad17 complex onto chromosomes. Phosphorylation of Ddc1 depends on the meiosis-specific kinase Mek1. In turn, Ddc1 promotes the stable association of Mek1 with chromosomes and is required for Mek1-dependent phosphorylation of the meiotic chromosomal protein Red1. Ddc1 therefore appears to operate in a positive feedback loop that promotes Mek1 function.