Rad51 is similar to RecA, both biochemically and structurally. It promotes homologous pairing and strand exchange within a regular nucleoprotein filament. In yeast, the Rad51 family of related proteins also includes Rad55, Rad57, and Dmc1. In mammalian cells, seven genes in this family have been identified (HsRAD51, XRCC2, XRCC3, RAD51B/hREC2 and HsDMC1, RAD51C, and RAD51D). Recent studies suggested that Rad51 is involved not only in homologous recombination but also in cell proliferation regulation.