Figure 4.

Structures of T4 gp45 clamp and the E. coli clamp loader, a protein comparable to T4 gp44/62 complex. A.) The three subunits of the gp45 clamp form a ring with the large opening lined with basic residues which interact with duplex DNA. The binding pocket for interacting with PIP box peptides is shown in yellow. B.) The E. coli γ complex is shown with the γ₃ subunits (yellow, green, and cyan), the δ' stator subunit (red), and the δ wrench subunit (blue). Also indicated are the regions of the E. coli γ complex which interact with the E. coli β clamp (orange) and the P-loop motifs for ATP binding (magenta).