Highlights
•  Bacterial proteins comprising solely a VRR-Nuc domain are dimeric in solution •  Bacterial VRR-Nuc domains act as Holliday-junction-resolving enzymes •  A conserved helical insertion in the FAN1 VRR-Nuc domain prevents dimerization •  FAN1 monomers cannot cleave Holliday junctions and instead cleave 5′ flap DNA

T