Efficient interaction of recA protein with fluorescent dye-labeled oligonucleotides.

Some fluorescein derivatives attached to the 5'-end of oligonucleotides stimulate recA protein-oligonucleotide binding. The complex formation at near stoichiometric DNA/protein ratios is demonstrated for 18-bases-long oligonucleotides. The complexes with dye-labeled oligonucleotides are shown to be active in the reaction of homologous strand exchange. The strand exchange reaction in the presence of adenosine-5'-O-(3-thiotriphosphate) proceeds with the formation of a stable complex of recA protein with the double stranded oligonucleotide, which is a product of the strand exchange. The displaced single-stranded oligonucleotide is shown to be bound weakly.