EFFICIENT INTERACTION OF RECA PROTEIN WITH FLUORESCENT DYE-LABELED OLIGONUCLEOTIDES

Some fluorescein derivatives attached to the 5'-end of oligonucleotide s stimulate recA protein-oligonucleotide binding. The complex formatio n at near stoichiometric DNA/protein ratios is demonstrated for 18-bas es-long oligonucleotides. The complexes with dye-labeled oligonucleoti des are shown to be active in the reaction of homologous strand exchan ge. The strand exchange reaction in the presence of adenosine-5'-O-(3- thiotriphosphate) proceeds with the formation of a stable complex of r ecA protein with the double stranded oligonucleotide, which is a produ ct of the strand exchange. The displaced single-stranded oligonucleoti de is shown to be bound weakly.