The exchange of the DNA binding protein RPA for the RAD51 recombinase on single-stranded DNA is a critical step in DNA break repair by homologous recombination. This RPA-RAD51 handoff is dependent on the tumor suppressor BRCA2. Importantly, our work has shown that the BRCA2-associated DSS1, a small, highly acidic protein, is also needed for this handoff process. Mechanistically, DSS1 acts as a DNA mimic to attenuate the affinity of RPA for DNA. Thus, by targeting RPA and mimicking DNA, DSS1 functions with BRCA2 in a two-component homologous recombination mediator complex in genome maintenance.