Bipartite stimulatory action of the Hop2–Mnd1 complex on the Rad51 recombinase

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Abstract
The HOP2 and MND1 genes are indispensable for meiotic recombination. The products of these genes associate to form a stable heterodimeric complex that binds DNA and stimulates the recombinase activity of Rad51 and Dmc1. Here we conduct molecular studies to delineate the action mechanism of the Hop2–Mnd1 complex. We present evidence to implicate Hop2 as the major DNA-binding subunit and Mnd1 as the prominent Rad51 interaction entity. Hop2–Mnd1 stabilizes the Rad51–single-stranded DNA (ssDNA) nucleoprotein filament, the catalytic intermediate in recombination reactions. We also show that Hop2–Mnd1 enhances the ability of the Rad51–ssDNA nucleoprotein filament to capture duplex DNA, an obligatory step in the formation of the synaptic complex critical for DNA joint formation. Thus, our results unveil a bipartite mechanism of Hop2–Mnd1 in homologous DNA pairing: stabilization of the Rad51 presynaptic filament and duplex DNA capture to enhance synaptic complex formation.