title: DnaG interacts with a linker region that joins the N- and C-domains of DnaB and induces the formation of 3-fold symmetric rings.
abstract: Loading of the replicative ring helicase onto the origin of replication (oriC) is the final outcome of a well coordinated series of events that collectively constitute a primosomal cascade. Once the ring helicase is loaded, it recruits the primase and signals the switch to the polymerization mode. The transient nature of the helicase-primase (DnaB-DnaG) interaction in the Escherichia coli system has hindered our efforts to elucidate its structure and function. Taking advantage of the stable DnaB-DnaG complex in Bacillus stearothermophilus, we have reviewed conflicting mutagenic data from other bacterial systems and shown that DnaG interacts with the flexible linker that connects the N- and C-terminal domains of DnaB. Furthermore, atomic force microscopy (AFM) imaging experiments show that binding of the primase to the helicase induces predominantly a 3-fold symmetric morphology to the hexameric ring. Overall, three DnaG molecules appear to interact with the hexameric ring helicase but a small number of complexes with two and even one DnaG molecule bound to DnaB were also detected. The structural/functional significance of these data is discussed and a speculative structural model for this complex is suggested.
authors.affiliation: Centre for Biomolecular Sciences (CBS), School of Pharmacy, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
authors.forename: Jenny
authors.initials: J
authors.lastname: Thirlway
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Turner
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Gibson
authors.forename: Laurence
authors.initials: L
authors.lastname: Gardiner
authors.forename: Kevin
authors.initials: K
authors.lastname: Brady
authors.forename: Stephanie
authors.initials: S
authors.lastname: Allen
authors.forename: Clive J
authors.initials: CJ
authors.lastname: Roberts
authors.forename: Panos
authors.initials: P
authors.lastname: Soultanas
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004265:DNA Helicases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D019915:DNA Primase / Q000378:metabolism* / Q000648:ultrastructure; D004261:DNA Replication; D053488:DnaB Helicases; D001411:Geobacillus stearothermophilus / Q000201:enzymology* / Q000235:genetics; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
chemical_list: D001426:Bacterial Proteins; D019915:DNA Primase; D004265:DNA Helicases; D053488:DnaB Helicases