Lecture 4

• Origins of replication – bacteria have one and eukaryotes have many on one chromosome. Initiator proteins bind to origins and recruit helicases. All initiator proteins are AAA+ ATPases.
• oriC


  245 bp sequence with multiple DnaA boxes (TTAT[C/A]CA[C/A]A)
• oriC


  • Has adjacent AT rich regions
• DnaA


  Binds to DnaA boxes
• DnaA self-association


  1. Binds to ATP

  2. Forms helical complex
• DNA wrapping around DnaA

  1. Bends DNA

  2. Unwinds adjacent AT-rich sequence
• DnaC helicase loader


  • Assembles onto hexameric DnaB helicase
  • Prepares DnaB to unwind DNA helix
• DnaC helicase loader binding

  1. Binds to DnaA protein complex at origin of replication

  2. Coordinates loading of DnaB helicase onto ssDNA region at origin
• DnaC loader dissociation


  1. DnaB unwinds helix

  2. Exposes ssRNA regions

  3. Bound by single-stranded binding proteins