title: RecR forms a ring-like tetramer that encircles dsDNA by forming a complex with RecF.
abstract: In the RecFOR pathway, the RecF and RecR proteins form a complex that binds to DNA and exerts multiple functions, including directing the loading of RecA onto single-stranded (ss) DNA regions near double-stranded (ds) DNA-ssDNA junctions and preventing it from forming a filament beyond the ssDNA region. However, neither the structure of the RecFR complex nor its DNA-binding mechanism was previously identified. Here, size-exclusion chromatography and small-angle X-ray scattering data indicate that Thermus thermophilus (tt) RecR binds to ttRecF to form a globular structure consisting of four ttRecR and two ttRecF monomers. In addition, a low resolution model shows a cavity in the central part of the complex, suggesting that ttRecR forms a ring-like tetramer inside the ttRecFR complex. Mutant ttRecR proteins lacking the N- or C-terminal interfaces that are required for tetramer formation are unable to form a complex with ttRecF. Furthermore, a ttRecFR complex containing the DNA-binding deficient ttRecR K23E/R27E double mutant, which contains mutations lying inside the ring, exhibits significantly reduced dsDNA binding. Thus, we propose that the ring-like ttRecR tetramer has a key role in tethering the ttRecFR complex onto dsDNA and that the ring structure may function as a clamp protein.
authors.affiliation: RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Honda
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Fujisawa
authors.forename: Takehiko
authors.initials: T
authors.lastname: Shibata
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Mikawa
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D053838:Scattering, Small Angle; D016963:Thermus thermophilus; D014961:X-Ray Diffraction
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C065831:RecR protein, Bacteria; D004247:DNA; C066218:recF protein, Bacteria