E. coli RuvA protein binds specifically to the Holliday structure which is the intermediate of recombination at the late stage of homologous recombination and recombination repair and forms a complex with RuvB motor protein allowing the migration of Holliday junction using ATP hydrolysis energy and expands the heteroduplex region. In solution, it forms a tetramer and binds to the cross-like DNA of the Holliday junction from below and above holding it in between (1, 2). The product is a recombinant protein abundantly expressed by E. coli and purified by methods such as chromatography (Fig. 1). The molecular weight is 22 kDa and even in solution, it binds to the Holliday structure and form a tetramer.