RPA directly stimulates Mer3/HFM1 helicase processivity to ensure normal crossover formation in meiosis

Altmannova, V.; Orlic, L.; Carrasco, C.; Adam, C.; Aicart-Ramos, C.; Guerini, D.; Borde, V.; Matos, J.; Moreno-Herrero, F.; Weir, J. R.

doi:10.1101/2025.08.02.668043

bioRxiv · 10.1101/2025.08.02.668043

RPA directly stimulates Mer3/HFM1 helicase processivity to ensure normal crossover formation in meiosis

Altmannova, V.·Orlic, L.·Carrasco, C.·Adam, C.·Aicart-Ramos, C.·Guerini, D.·Borde, V.·Matos, J.·Moreno-Herrero, F.·Weir, J. R.

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Abstract

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 exhibit reduced crossover frequencies and accumulate unresolved recombination intermediates during budding yeast meiosis. Via genome-wide localisation experiments, we link this effect to a weakened recruitment to double-strand break sites of the mer3 mutant. 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.

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Altmannova, V., Orlic, L., Carrasco, C., Adam, C., Aicart-Ramos, C., Guerini, D., Borde, V., Matos, J., Moreno-Herrero, F., Weir, J. R.. 2025-08-02. RPA directly stimulates Mer3/HFM1 helicase processivity to ensure normal crossover formation in meiosis. https://doi.org/10.1101/2025.08.02.668043

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