Figure 7.

Model indicating how Mek1 and Ndt80 negatively feedback on each other. DSBs activate the Mec1/Tel1 checkpoint kinases, which in turn activates Mek1. Mek1^H indicates a level of kinase activity above the threshold necessary to inactivate Ndt80. Mek1 inhibits Rad51-mediated DSB repair by phosphorylation of Rad54 and Hed1 and promotes the ZMM pathway of interhomolog DSB repair leading to interfering crossovers and synapsis. As a result of this repair, Mek1 kinase activity is lowered below the threshold necessary to inactivate Ndt80 (Mek1^L). Induction of NDT80 results in transcription of CDC5, leading to Holliday junction resolution and SC disassembly via Red1 and Zip1 degradation. As a result, the remaining Mek1 is inactivated, allowing Rad51-mediated repair of any residual DSBs. In addition, Ndt80-mediated transcription of CLB1 allows meiotic progression. DSB, double strand break; SC, synaptonemal complex.