['The basic molecular mechanisms that govern the search for DNA homology and subsequent homologous pairing during genetic recombination are not understood. RecA is the central homologous recombination protein of Escherichia coli; because several RecA homologues have been identified in eukaryotic cells, it is likely that the mechanisms employed by RecA are conserved throughout evolution. Analysis of the kinetics of the homologous search and pairing reactions catalyzed by RecA should therefore provide insights of general relevance into the mechanisms by which macromolecules locate, and interact with, specific DNA targets.', 'RecA forms three-stranded synaptic complexes with a single-stranded oligonucleotide and a homologous region in duplex DNA. The kinetics of this initial pairing reaction were characterized using duplex DNA molecules of various concentrations and complexities containing a single target site, as well as various concentrations of homologous single-stranded oligonucleotides. The formation of the synaptic complex follows apparent second-order reaction kinetics with a rate proportional to the concentrations of both the homologous single-stranded oligonucleotide and the target sites within the duplex DNA. The reaction rate is independent of the complexity of duplex DNA in the reaction. We propose a kinetic scheme in which the RecA-single-stranded DNA filament interacts with duplex DNA and locates its target in a relatively fast reaction. We also suggest that complex conformational changes occur during the subsequent rate-limiting step.'] Does the search for DNA homology limit stable homologous pairing promoted by RecA protein?