Phosphorylation of cohesin Rec11/SA3 by casein kinase 1 promotes homologous recombination by assembling the meiotic chromosome axis.

In meiosis, cohesin is required for sister chromatid cohesion, as well as meiotic chromosome axis assembly and recombination. However, mechanisms underlying the multifunctional nature of cohesin remain elusive. Here, we show that fission yeast casein kinase 1 (CK1) plays a crucial role in assembling the meiotic chromosome axis (so-called linear element: LinE) and promoting recombination. An in vitro phosphorylation screening assay identified meiotic cohesin subunit Rec11/SA3 as an excellent substrate of CK1. The phosphorylation of Rec11 by CK1 mediates the interaction with the Rec10/Red1/SCP2 axis component, a key step in meiotic chromosome axis assembly, and is dispensable for sister chromatid cohesion. Crucially, the expression of Rec11-Rec10 fusion protein nearly completely bypasses the requirement for CK1 or cohesin phosphorylation for LinE assembly and recombination. This study uncovers a central mechanism of the cohesin-dependent assembly of the meiotic chromosome axis and recombination apparatus that acts independently of sister chromatid cohesion.