Cdc7-dependent phosphorylation of Mer2 facilitates initiation of yeast meiotic recombination

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Abstract
Meiosis ensures genetic diversification of gametes and sexual reproduction. For successful meiosis, multiple events such as DNA replication, recombination, and chromosome segregation must occur coordinately in a strict regulated order. We investigated the meiotic roles of Cdc7 kinase in the initiation of meiotic recombination, namely, DNA double-strand breaks (DSBs) mediated by Spo11 and other coactivating proteins. Genetic analysis using bob1-1 cdc7Δ reveals that Cdc7 is essential for meiotic DSBs and meiosis I progression. We also demonstrate that the N-terminal region of Mer2, a Spo11 ancillary protein required for DSB formation and phosphorylated by cyclin-dependent kinase (CDK), contains two types of Cdc7-dependent phosphorylation sites near the CDK site (Ser30): One (Ser29) is essential for meiotic DSB formation, and the others exhibit a cumulative effect to facilitate DSB formation. Importantly, mutations on these sites confer severe defects in DSB formation even when the CDK phosphorylation is present at Ser30. Diploids of cdc7Δ display defects in the chromatin binding of not only Spo11 but also Rec114 and Mei4, other meiotic coactivators that may assist Spo11 binding to DSB hot spots. We thus propose that Cdc7, in concert with CDK, regulates Spo11 loading to DSB sites via Mer2 phosphorylation.