4gx8
Crystal structure of a DNA polymerase III alpha-epsilon chimera
Structural highlights
FunctionDPO3A_ECOLI DNA polymerase III is a complex, multichain enzyme responsible for most of the replicative synthesis in bacteria. This DNA polymerase also exhibits 3' to 5' exonuclease activity. The alpha chain is the DNA polymerase.DPO3E_ECOLI DNA polymerase III is a complex, multichain enzyme responsible for most of the replicative synthesis in bacteria. The epsilon subunit contain the editing function and is a proofreading 3'-5' exonuclease. Publication Abstract from PubMedA complex of the three (alphaepsilontheta) core subunits and the beta2 sliding clamp is responsible for DNA synthesis by Pol III, the Escherichia coli chromosomal DNA replicase. The 1.7 A crystal structure of a complex between the PHP domain of alpha (polymerase) and the C-terminal segment of epsilon (proofreading exonuclease) subunits shows that epsilon is attached to alpha at a site far from the polymerase active site. Both alpha and epsilon contain clamp-binding motifs (CBMs) that interact simultaneously with beta2 in the polymerization mode of DNA replication by Pol III. Strengthening of both CBMs enables isolation of stable alphaepsilontheta:beta2 complexes. Nuclear magnetic resonance experiments with reconstituted alphaepsilontheta:beta2 demonstrate retention of high mobility of a segment of 22 residues in the linker that connects the exonuclease domain of epsilon with its alpha-binding segment. In spite of this, small-angle X-ray scattering data show that the isolated complex with strengthened CBMs has a compact, but still flexible, structure. Photo-crosslinking with p-benzoyl-L-phenylalanine incorporated at different sites in the alpha-PHP domain confirm the conformational variability of the tether. Structural models of the alphaepsilontheta:beta2 replicase complex with primer-template DNA combine all available structural data. Proofreading exonuclease on a tether: the complex between the E. coli DNA polymerase III subunits alpha, {varepsilon}, theta and beta reveals a highly flexible arrangement of the proofreading domain.,Ozawa K, Horan NP, Robinson A, Yagi H, Hill FR, Jergic S, Xu ZQ, Loscha KV, Li N, Tehei M, Oakley AJ, Otting G, Huber T, Dixon NE Nucleic Acids Res. 2013 Apr 10. PMID:23580545[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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