Rad51 is an accessory factor for Dmc1-mediated joint molecule formation during meiosis.

Meiotic recombination in budding yeast requires two RecA-related proteins, Rad51 and Dmc1, both of which form filaments on DNA capable of directing homology search and catalyzing formation of homologous joint molecules (JMs) and strand exchange. With use of a separation-of-function mutant form of Rad51 that retains filament-forming but not JM-forming activity, we show that the JM activity of Rad51 is fully dispensable for meiotic recombination. The corresponding mutation in Dmc1 causes a profound recombination defect, demonstrating Dmc1's JM activity alone is responsible for meiotic recombination. We further provide biochemical evidence that Rad51 acts with Mei5-Sae3 as a Dmc1 accessory factor. Thus, Rad51 is a multifunctional protein that catalyzes recombination directly in mitosis and indirectly, via Dmc1, during meiosis.