DnaG interacts with a linker region that joins the N‐ and C‐domains of DnaB and induces the formation of 3‐fold symmetric rings

• Published in: Nucleic acids research Vol. 32; no. 10; pp. 2977 - 2986
• Main Authors: Thirlway, Jenny, Turner, Ian J., Gibson, Christopher T., Gardiner, Laurence, Brady, Kevin, Allen, Stephanie, Roberts, Clive J., Soultanas, Panos
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 2004; Oxford Publishing Limited (England)
• Subjects: Bacillus stearothermophilus; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; DNA Helicases - chemistry; DNA Helicases - genetics; DNA Helicases - metabolism; DNA Helicases - ultrastructure; DNA Primase - metabolism; DNA Primase - ultrastructure; DNA Replication; DnaB Helicases; Escherichia coli; Geobacillus stearothermophilus - enzymology; Geobacillus stearothermophilus - genetics; Microscopy, Atomic Force; Models, Molecular; Mutation - genetics; Protein Binding; Protein Structure, Quaternary; Protein Structure, Tertiary
• ISSN: 0305-1048; 1362-4962; 1362-4962
• DOI: 10.1093/nar/gkh628

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.