Late Steps in Genetic Recombination: Branch Migration and Holliday Junction Resolution by RuvA, RuvB, and RuvC Proteins

The process of genetic recombination requires efficient catalysis of a number of defined biochemical reactions including (1) synapsis, the pairing of homologous DNA molecules; (2) heteroduplex formation, as the DNA strands are switched from one molecule to another; and (3) resolution, by which the crossovers are cut to release recombinant molecules (for reviews, see Radding 1982; West 1992). Detailed biochemical studies of the RecA protein of Escherichia coli have led to an increased understanding of the molecular processes involved in DNA pairing and the formation of a heteroduplex joint by strand exchange (Cox and Lehman 1987; Kowalczykowski 1991; Radding 1991; West 1992), but until quite recently, little was known about the enzymes or mechanisms by which the joints (or Holliday junctions) are moved along DNA by a process akin to branch migration or by which they are resolved.