title: Chaperone-mediated reduction of RepA dimerization is associated with RepA conformational change.
abstract: RepA, the initiator protein of plasmid P1, binds to multiple sites (iterons) in the origin. The binding normally requires participation of chaperones, DnaJ, DnaK and GrpE. When purified, RepA appears dimeric and is inactive in iteron binding. On reaction with chaperones, a species active in iteron binding is formed and found to be monomeric. To test whether the chaperones can reduce dimerization, RepA was used to replace the dimerization domain of the lambda repressor. The hybrid protein repressed the lambda operator efficiently, indicating that RepA can dimerize in vivo. A further increase in repressor activity was seen in dnaJ mutant cells. These results are consistent with a chaperone-mediated reduction of RepA dimerization. We also found that RepA mutants defective in dimerization still depend on DnaJ for iteron binding. Conversely, RepA mutants that no longer require chaperones for iteron binding remain dimerization proficient. These results indicate that the chaperone dependence of RepA activity is not solely owing to RepA dimerization. Our results are most simply explained by a chaperone-mediated conformational change in RepA protomer that activates iteron binding. This conformational change also results in reduced RepA dimerization.
authors.affiliation: Laboratory of Biochemistry, NCI, NIH, Bethesda, MD 20892-4255, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Dibbens
authors.forename: K
authors.initials: K
authors.lastname: Muraiso
authors.forename: D K
authors.initials: DK
authors.lastname: Chattoraj
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism; D001665:Binding Sites; D018983:DNA Footprinting; D004265:DNA Helicases; D004274:DNA, Recombinant; D004268:DNA-Binding Proteins; D019281:Dimerization; D050956:HSP40 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism / Q000494:pharmacology; D008956:Models, Chemical; D018832:Molecular Chaperones / Q000378:metabolism* / Q000494:pharmacology; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D011487:Protein Conformation; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics; D015534:Trans-Activators; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D001426:Bacterial Proteins; D004274:DNA, Recombinant; D004268:DNA-Binding Proteins; D050956:HSP40 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D011506:Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins; C045264:replication initiator protein; D004265:DNA Helicases