Recombination Machinery: Holliday Junction-Resolving Enzymes

Holliday junctions are resolved into recombinant duplex DNA species by a class of structure-specific endonucleases known as the Holliday junction-resolving enzymes. The primary cellular resolving enzyme in bacteria is RuvC, which is the main focus of this chapter. The author also talks about the RusA protein, which may act as an alternative to RuvC in some bacterial species, and attempts to place RuvC in a wider context based on our knowledge of other junction-resolving enzymes. The first cellular Holliday junction-resolving enzyme identified was RuvC from Escherichia coli. Homologous recombination is ubiquitous among cellular life forms and many prokaryotic and eukaryotic viruses, and wherever Holliday junctions are formed, junction-resolving enzymes can be confidently expected. Resolving enzymes recognize the branched structure of the Holliday junction and introduce paired phosphodiester bond cleavages in opposing strands to collapse the junction, releasing nicked duplex DNA products. The study of homologous recombination and the Holliday junction was for many years the realm of geneticists. Holliday junction migration work has largely been driven by studies of the E. coli RuvABC resolvasome, emphasizing the continuing utility of bacteria as a model system to study some of the most interesting problems in biology.