RPA directly stimulates Mer3 helicase processivity to ensure normal crossover formation in meiosis
- Veronika Altmannova
- Lucija Orlić
- Carolina Carrasco
- Céline Adam
- Clara Aicart-Ramos
- Dario Guerrini
- Petra Janning
- Valérie Borde
- Joao Matos
- Fernando Moreno-Herrero
- John R. Weir
2026-03-18
Meiotic crossover formation is critical for generating viable gametes and enhancing genetic diversity. The helicase Mer3 (HFM1 in humans) is a highly conserved factor essential for promoting crossovers and ensuring their proper distribution. Here, we identify replication protein A (RPA) as a direct interactor of budding yeast Mer3. We demonstrate that this interaction is conserved between human HFM1 and RPA. Cross-linking mass spectrometry and structural modelling with AlphaFold2 reveal a conserved and specific Mer3-RPA interface. Single-molecule magnetic tweezers assays demonstrate that direct RPA interaction is required for Mer3 helicase processivity under conditions of low DNA tension. Consistently, a mer3 mutant deficient in RPA binding exhibits reduced crossover frequencies and accumulates unresolved recombination intermediates during budding yeast meiosis. Via genome-wide localisation experiments, we link this effect to weakened recruitment of the mer3 mutant to double-strand break sites. Our findings provide mechanistic insights into coordination of meiotic recombination by the Mer3 helicase through interactions with the canonical DNA repair machinery, highlighting a conserved mechanism underlying crossover control during sexual reproduction.