Mei5-Sae3 stabilizes both active and inactive forms of Dmc1 filaments independently of its impact on ATP hydrolysis.

In budding yeast, Dmc1's recombinogenic activity is controlled by the meiosis-specific heterodimer Mei5-Sae3. Mei5-Sae3 is required for assembly of Dmc1 at sites of meiotic DNA double-stranded breaks. Here, we report Mei5-Sae3 can stabilize Dmc1 filaments in both the active and inactive allosteric conformations depending on the nucleotide cofactor supporting filament formation. Mei5-Sae3 specifically stabilizes the active filament form without inhibiting ATP hydrolysis, in contrast to high concentrations of calcium, AMP-PNP, and the E157D mutation in Dmc1, each of which promotes Dmc1 filament stability by processes that include blocks to ATP hydrolysis. Mei5-Sae3 increases Dmc1 ATP hydrolysis by a mechanism that could be a cause of active filament stabilization or a secondary and inconsequential effect of active filament stabilization. Mei5-Sae3 can also stabilize filaments in the inactive conformation with ADP as a cofactor. These results show that Mei5-Sae3's filament stabilization activity does not fully depend on alteration of the hydrolytic cycle. We also show Dmc1-E157D, a gain-of-function protein that bypasses the requirement for Mei5-Sae3 in vivo, is defective in ATPase activity and stabilizes the active form of Dmc1 filaments as predicted by previous observations. Hence, Dmc1's homology search and strand exchange activities do not depend on its ability to hydrolyze ATP.