Abstract
Homologous recombination (HR) is a universally conserved DNA repair pathway that can result in the exchange of genetic material. In eukaryotes, HR has evolved into an essential step in meiosis. During meiosis many eukaryotes utilize a two-recombinase pathway. This system consists of Rad51 and the meiosis-specific recombinase Dmc1. Both recombinases have distinct activities during meiotic HR, despite being highly similar in sequence and having closely related biochemical activities, raising the question of how these two proteins can perform separate functions. A likely explanation for their differential regulation involves the meiosis-specific recombination proteins Hop2 and Mnd1, which are part of a highly conserved eukaryotic protein complex that participates in HR, albeit through poorly understood mechanisms. To better understand how Hop2-Mnd1 functions during HR, here we used DNA curtains in conjunction with single-molecule imaging to measure and quantify the binding of the Hop2-Mnd1 complex from Saccharomyces cerevisiae to recombination intermediates comprising Rad51- and Dmc1-ssDNA in real time. We found that yeast Hop2-Mnd1 bound rapidly to Dmc1-ssDNA filaments with high affinity and remained bound for ∼1.3 min before dissociating. We also observed that this binding interaction was highly specific for Dmc1 and found no evidence for an association of Hop2-Mnd1 with Rad51-ssDNA or RPA-ssDNA. Our findings provide new quantitative insights into the binding dynamics of Hop2-Mnd1 with the meiotic presynaptic complex. On the basis of these findings, we propose a model in which recombinase specificities for meiotic accessory proteins enhance separation of the recombinases' functions during meiotic HR.