Rad51 is a recombinase that is essential for homologous recombination and double-strand break repair. It binds to single and double-stranded DNA, and has DNA-dependent ATPase activity. Rad51 unwinds duplex DNA and forms helical nucleoprotein filaments in a manner that is controlled through the action of DNA helicases that counteract nucleofilament formation. Rad51 interacts with BRCA1 and BRCA2, and also plays a role in p53-mediated signalling. Interaction of Rad51 with Chk1 kinase may occur in response to Chk1 phosphorylation.