title: SSB antagonizes RecX-RecA interaction.
abstract: The RecX protein of Escherichia coli inhibits the extension of RecA protein filaments on DNA, presumably by binding to and blocking the growing filament end. The direct binding of RecX protein to single-stranded DNA is weak, and previous reports suggested that direct binding to DNA did not explain the effects of RecX. We now demonstrate that elevated concentrations of SSB greatly moderate the effects of RecX protein. High concentrations of the yeast RPA protein have the same effect, suggesting that the effect is not species-specific or even specific to bacterial SSB proteins. A direct SSB-RecX interaction is thus unlikely. We suggest that SSB is blocking access to single-stranded DNA. The evident competition between RecX and SSB implies that the mechanism of RecX action may involve RecX binding to both RecA protein and to DNA. We speculate that the interaction of RecX protein and RecA may enable an enhanced DNA binding by RecX protein. The effects of SSB are increased if the SSB C terminus is removed.
authors.affiliation: Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706-1544, USA.
authors.forename: Dmitry M
authors.initials: DM
authors.lastname: Baitin
authors.forename: Marielle C
authors.initials: MC
authors.lastname: Gruenig
authors.forename: Michael M
authors.initials: MM
authors.lastname: Cox
mesh_terms: D001426:Bacterial Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D010084:Oxidation-Reduction; D011071:Poly T / Q000378:metabolism; D011485:Protein Binding; D011938:Rec A Recombinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C430523:RecX protein, Xanthomonas campestris; C476430:SSB protein, E coli; D011071:Poly T; D011938:Rec A Recombinases