Evolutionary conservation of the structure and function of meiotic Rec114-Mei4 and Mer2 complexes

Meiosis-specific Rec114-Mei4 and Mer2 complexes are thought to enable Spo11-mediated DNA double-strand-break (DSB) formation through a mechanism that involves DNA-dependent condensation. However, the structure, molecular properties, and evolutionary conservation of Rec114-Mei4 and Mer2 are unclear. Here, we present AlphaFold structures of Rec114-Mei4 and Mer2 complexes, supported by nuclear magnetic resonance (NMR) spectroscopy, small-angle X-ray scattering (SAXS), and mutagenesis. We show that dimers composed of the Rec114 C-terminus form -helical chains that cup an N-terminal Mei4 -helix, and that Mer2 forms a parallel homotetrameric coiled coil. Both Rec114-Mei4 and Mer2 bind preferentially to branched DNA substrates, indicative of multivalent protein-DNA interactions. Indeed, the Rec114-Mei4 interaction domain contains two DNA-binding sites that point in opposite directions and drive condensation. The Mer2 coiled-coil domain bridges co-aligned DNA duplexes, likely through extensive electrostatic interactions along the length of the coiled coil. Finally, we show that the structure of Rec114-Mei4 and Mer2 are conserved across eukaryotes, while DNA-binding properties vary significantly. This work provides insights into the mechanism whereby Rec114-Mei4 and Mer2 complexes promote the assembly of the meiotic DSB machinery, and suggests a model where Mer2 condensation is the essential driver of assembly, with the DNA-binding activity of Rec114-Mei4 playing a supportive role.