 The proteins of the RecA recombinase family of proteins are thought to be descended from a common ancestral recombinase . The RecA recombinase family contains RecA protein from bacteria , the Rad51 and Dmc1 proteins from eukaryotes , and RadA from archaea , and the recombinase paralog proteins . Studies modeling the evolutionary relationships between the Rad51 , Dmc1 and RadA proteins indicate that they are monophyletic , or that they share a common molecular ancestor . Within this protein family , Rad51 and Dmc1 are grouped together in a separate clade from RadA . One of the reasons for grouping these three proteins together is that they all possess a modified helix @-@ turn @-@ helix motif , which helps the proteins bind to DNA , toward their N @-@ terminal ends . An ancient gene duplication event of a eukaryotic RecA gene and subsequent mutation has been proposed as a likely origin of the modern RAD51 and DMC1 genes . 
