Stoichiometry, base orientation, and nuclease accessibility of RecA.DNA complexes seen by polarized light in flow-oriented solution. Implications for the mechanism of genetic recombination.

By using flow linear dichroism, in combination with nuclease digestion and two spectroscopically distinguishable DNAs, we demonstrate the existence of two internal and one external DNA-binding sites in the RecA fiber. A number of different complexes between RecA and single- and double-stranded DNAs are characterized with respect to stoichiometry, location, and base orientation of each of the associated DNAs. Based on these results, we discuss important steps of the mechanism of general genetic recombination.