“The highly conserved Cdc7-Dbf4 cell cycle kinase regulates crossover formation in meiotic yeast cells’’

Interhomolog crossovers promote proper chromosome segregation during meiosis and are formed by the highly regulated repair of programmed double strand breaks. This regulation requires components of the synaptonemal complex, a proteinaceous structure that forms between homologous chromosomes. In yeast, synaptonemal complex formation requires genes encoding a diverse set of “ZMM” proteins, including the transverse filament protein, Zip1. These proteins also promote the biased resolution of recombination intermediates into crossovers that are distributed throughout the genome by interference. In contrast, non-crossovers are formed primarily through synthesis-dependent strand annealing mediated by the Sgs1 helicase. An unbiased biochemical approach revealed phosphorylation sites in the C terminus of Zip1 that are required for its pro-crossover function of protecting recombination intermediates from Sgs1. Zip1 is a direct substrate of the conserved Cdc7-Dbf4 (DDK) cell cycle kinase. DDK phosphorylation of Zip1 is dependent upon Mek1, a kinase required for interhomolog bias, suggesting a link by which interhomolog bias and the crossover/noncrossover decision can be coordinated.