E. coli Holliday junction complex. Molecular model of a RuvA protein (red) in complex with a Holliday junction between homologous strands of DNA (deoxyribonucleic acid, blue) from an E. coli (Escherichia coli) bacterium. A Holliday junction forms during crossing over, a natural genetic process that occurs between homologous chromosomes and leads to the switching of genetic material between the chromosomes. This recombination increases the genetic variation in a population. RuvA is part of the RuvABC complex of three proteins that mediate branch migration and resolve the Holliday junction created during homologous recombination in bacteria.