Endonuclease that resolves Holliday junction intermediates. Promotes DNA repair. Exhibits sequence and structure-selective cleavage of four-way DNA junctions, where it introduces symmetrical nicks in two strands of the same polarity, though it can also cut branched DNA structures that lack the symmetry of Holliday junctions. Endonucleolytic cleavage at a junction such as a reciprocal single-stranded crossover between two homologous DNA duplexes (Holliday junction). Binds 1 Mg(2+) ion per subunit. Homodimer. Belongs to the RusA family.