title: Recognition of duplex DNA containing single-stranded regions by recA protein.
abstract: Genetic recombination in Escherichia coli requires recA protein, the product of the recA+ gene. In this paper we show that purified recA protein, which binds strongly to denatured DNA, cooperatively recognizes DNA containing short single-stranded regions. The interaction of varying amounts of recA protein with DNA molecules was investigated by measuring its DNA-dependent ATPase activity. In 3mM Mg2+, the ATPase activity was stimulated by excess single-stranded DNA and was minimal with either intact circular or blunt-ended linear duplexes. Single-strand gaps of about 30 nucleotides were sufficient to increase the ATPase activity to a level almost as great as that observed with single-stranded DNA. Sedimentation studies at neutral pH showed cooperative binding of recA protein to single-stranded DNA or to duplex DNA containing single-stranded regions. In the presence of ATP, an intermediate rate of sedimentation was observed; in contrast, adenosine 5'-gamma-thiotriphosphate (ATP[S]) caused the formation of fast-sedimenting DNA-protein complexes. Gapped plasmid DNA plus recA protein and ATP[S] formed large aggregates containing thousands of molecules. Complex formation and stimulation of the ATPase activity of recA protein with duplex DNA containing single-stranded regions indicates that recA protein may change the conformation of the normally duplex molecules to a conformation prepared for homologous pairing.
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics*; D002352:Carrier Proteins / Q000235:genetics*; D004269:DNA, Bacterial / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000378:metabolism*; D004279:DNA, Viral / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D008854:Microscopy, Electron; D011938:Rec A Recombinases; D011995:Recombination, Genetic; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D004279:DNA, Viral; D011938:Rec A Recombinases; D000251:Adenosine Triphosphatases