Regulation of Hed1 and Rad54 binding during maturation of the meiosis‐specific presynaptic complex

Most eukaryotes have two Rad51/RecA family recombinases, Rad51, which promotes recombination during mitotic double‐strand break (DSB) repair, and the meiosis‐specific recombinase Dmc1. During meiosis, the strand exchange activity of Rad51 is downregulated through interactions with the meiosis‐specific protein Hed1, which helps ensure that strand exchange is driven by Dmc1 instead of Rad51. Hed1 acts by preventing Rad51 from interacting with Rad54, a cofactor required for promoting strand exchange during homologous recombination. However, we have a poor quantitative understanding of the regulatory interplay between these proteins. Here, we use real‐time single‐molecule imaging to probe how the Hed1‐ and Rad54‐mediated regulatory network contributes to the identity of mitotic and meiotic presynaptic complexes. Based on our findings, we define a model in which kinetic competition between Hed1 and Rad54 helps define the functional identity of the presynaptic complex as cells undergo the transition from mitotic to meiotic repair.