Periodicity in recA protein-DNA complexes.

The reaction of guanine residues with dimethylsulfate was studied for complexes of recA protein with fluorescent dye tagged double stranded oligonucleotides. The patterns of dimethylsulfate modification obtained demonstrate a similarity of DNA states in the complexes with recA protein formed as a result of recA promoted strand exchange and renaturation reactions. The guanine modification efficiency varies periodically as a function of the base position along the oligonucleotide axis, with a period of 3 nucleotides. This effect suggests that the arrangement of recA monomers along the oligonucleotide is strictly ordered, and the dimethylsulfate reactivity of a guanine residue depends on the site of its binding in a recA monomer.