Cryo-EM Structures of E. coli Clamp Loader Complexes

The clamp loader complex loads the circular sliding clamps onto the primer-template DNA during replication, enabling the polymerase to copy an extremely large number of nucleotides in a single binding event and enabling replication to occur with high speed and fidelity. Previous studies on the structure of the clamp loader complex have provided significant insights on the functions and interaction between various domains of its subunits with the DNA and with other proteins of the DNA polymerase III holoenzyme. However, previous methods of obtaining the structure of the clamp loader limited the information required to truly understand the dynamic nature of this protein complex. With the help of cryo-electron microscopy, a relatively new technique that helps to image molecules in their native state by freezing them in thin vitreous ice, we study the structures of this protein complex to gain more insights and observe the different dynamic states of this protein complex, to be able to better explain the interaction between different subunits as well as other replicative proteins, enzymes, and the DNA.