Plays an important role in homologous strand exchange, a key step in DNA repair through homologous recombination (HR). Binds to single-stranded DNA in an ATP-dependent manner to form nucleoprotein filaments which are essential for the homology search and strand exchange. Catalyzes the recognition of homology and strand exchange between homologous DNA partners to form a joint molecule between a processed DNA break and the repair template. Recruited to resolve stalled replication forks during replication stress. Also involved in interstrand cross-link repair. Forms linear homooligomers, giving rise to a RAD51 nucleoprotein filament, which is essential for strand-pairing reactions during DNA recombination. Accumulated at sites of DNA damage. Recruited to stalled replication forks during replication stress. Expressed at high levels in lymphoid and reproductive organs. Belongs to the RecA family. RAD51 subfamily.