Hop2-Mnd1 functions as a DNA sequence fidelity switch in Dmc1-mediated DNA recombination

Homologous recombination during meiosis is critical for chromosome segregation and also gives rise to genetic diversity. Genetic exchange between homologous chromosomes during meiosis is mediated by the recombinase Dmc1, which is capable of recombining DNA sequences with mismatches. The Hop2-Mnd1 complex mediates Dmc1 activity. Here, we reveal a regulatory role for Hop2-Mnd1 in restricting substrate selection. Specifically, Hop2-Mnd1 upregulates Dmc1 activity with DNA substrates that are either fully homologous or contain DNA mismatches, and it also acts against DNA strand exchange between substrates solely harboring microhomology. By isolating and examining salient Hop2-Mnd1 separation-of-function variants, we show that suppressing illegitimate DNA recombination requires the Dmc1 filament interaction attributable to Hop2-Mnd1 but not its DNA binding activity. Our study provides mechanistic insights into how Hop2-Mnd1 helps maintain meiotic recombination fidelity.