Homologous recombination (HR) is critically important for genome maintenance, including the repair of DNA double-strand breaks. The Rad51 recombinase plays a central role in the HR pathway. The assembly of Rad51 presynaptic filament is one of the most crucial steps in HR since homology search and subsequent DNA joint formation is accomplished in the context of the Rad51 filament. This process is subject to regulation by a variety of factors such as single-strand DNA binding protein, replication protein A (RPA) and the DNA helicase Srs2. In chapter II of this dissertation, I discuss the molecular properties of the yeast mediator protein Rad52 that promotes Rad51 filament formation when RPA is present. Specifically, the functional significance of novel Rad52 interactions with DNA and protein partners has been examined in the in vivo and in vitro settings to provide a mechanistic basis for the multi-faceted role of the Rad52 in the regulation of Rad51. In chapter III, I describe the biochemical characterization of rad51 mutants that are defective in interaction with either Rad52 or Srs2. The relevance of Rad51 interaction with Rad52 and Srs2 in the assembly of Rad51 filament has been defined through the analyses of these mutants. The results from my thesis research provide insights into the regulation of the Rad51 recombinase activity.