Two RecA homologs, Rad51 and the meiosis-specific Dmc1, coat single-stranded 3' ends of DNA produced by resection of double-strand breaks. Rad51 and Dmc1 interact and colocalize to the same early recombination nodules (Ashley et al. 1995, Ikeya et al. 1996, Plug et al. 1996, Barlow et al. 1997, Barlow et al. 1998, Tarsounas et al. 1999, Moens et al. 2007). Knockouts of Dmc1 abolish recombination and synapsis therefore Rad51 is not sufficient for recombination (Pittman et al. 1998, Yoshida et al. 1998).
Immunocytology shows the Rpa heterotrimer arrives at recombination nodules with or after Rad51 and Dmc1 (Plug et al. 1998, Plug et al. 1997, Moens et al. 2007). Rpa also co-localizes with Atm (Plug et al. 1997). The checkpoint kinase Cdk4 colocalizes with Rpa (Ashley et al. 2001).
Brca1 and Brca2 are found extensively distributed on synaptonemal complexes. Results from knockout mice indicate that Brca2, Rad51C, and Tex15 participate in loading Rad51 and Dmc1 onto single-stranded DNA (Kuznetsov et al. 2007, Yang et al. 2008). Brca1 participates in loading Rad51 but not Dmc1.