cryo-EM structures of the <i>E. coli</i> replicative DNA polymerase reveal its dynamic interactions with the DNA sliding clamp, exonuclease and <b>τ</b>.
basic_science · Level V
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- Record sourced from PubMed, PMID 26499492.
- Also identified by DOI 10.7554/eLife.11134 and PMC identifier 4703070.
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Abstract
The replicative DNA polymerase PolIIIα from <i>Escherichia coli</i> is a uniquely fast and processive enzyme. For its activity it relies on the DNA sliding clamp β, the proofreading exonuclease ε and the C-terminal domain of the clamp loader subunit τ. Due to the dynamic nature of the four-protein complex it has long been refractory to structural characterization. Here we present the 8 Å resolution cryo-electron microscopy structures of DNA-bound and DNA-free states of the PolIII-clamp-exonuclease-τ<sub>c</sub> complex. The structures show how the polymerase is tethered to the DNA through multiple contacts with the clamp and exonuclease. A novel contact between the polymerase and clamp is made in the DNA bound state, facilitated by a large movement of the polymerase tail domain and τ<sub>c</sub>. These structures provide crucial insights into the organization of the catalytic core of the replisome and form an important step towards determining the structure of the complete holoenzyme.