The complex of Rad51B and Rad51C binds single-stranded DNA and hydrolyses ATP (Sigurdsson et al. 2001). Rad51B and Rad51C are both required for recombination and DNA double-strand break repair in vivo. The complex cannot substitute for RPA but enhances Rad51/RPA mediated repair. The proposed mechanism for this is that Rad51b:Rad51C partially overcomes the suppressive effect of RPA on Rad51-catalyzed DNA pairing and strand exchange; RPA is an important accessory factor for Rad51-mediated homologous DNA pairing and strand exchange, but it can also compete with Rad51 for binding sites on the ssDNA template, which, when allowed to occur, suppresses pairing and strand exchange efficiency markedly (Sung et al. 2000).