Homologous recombination is an ubiquitous process that shapes genomes and repairs DNA damage. The reaction is classically divided into three phases: presynaptic, synaptic, and postsynaptic. In Escherichia coli, the presynaptic phase involves either RecBCD or RecFOR
proteins, which act on
DNA double-stranded ends and
DNA single-stranded gaps, respectively; the central synaptic steps are catalyzed by the ubiquitous
DNA-binding protein RecA; and the postsynaptic phase involves either RuvABC or RecG
proteins, which catalyze branch-migration and, in the case of RuvABC, the cleavage of
Holliday junctions. Here, we review the biochemical properties of these molecular machines and analyze how, in light of these properties, the phenotypes of null mutants allow us to define their
biological function(s). The consequences of point mutations on the biochemical properties of recombination
enzymes and on cell phenotypes help refine the molecular mechanisms of action and the
biological roles of recombination
proteins. Given the high level of conservation of key
proteins like RecA and the conservation of the principles of action of all recombination
proteins, the deep knowledge acquired during decades of studies of homologous recombination in bacteria is the foundation of our present understanding of the processes that govern
genome stability and evolution in all living organisms.