Structural highlights
Function[DPO3B_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 beta chain is required for initiation of replication once it is clamped onto DNA, it slides freely (bidirectional and ATP-independent) along duplex DNA. Publication Abstract from PubMedClamp loaders load ring-shaped sliding clamps onto DNA. Once loaded onto DNA, sliding clamps bind to DNA polymerases to increase the processivity of DNA synthesis. To load clamps onto DNA, an open clamp loader-clamp complex must form. An unresolved question is whether clamp loaders capture clamps that have transiently opened, or whether clamp loaders bind closed clamps and actively open clamps. A simple fluorescence-based clamp opening assay was developed to address this question, and to determine how ATP binding contributes to clamp opening. A direct comparison of real time binding and opening reactions revealed that the Escherichia coli gamma complex binds beta first, and then opens the clamp. Mutation of conserved arginine fingers in the gamma complex that interact with bound ATP decreased clamp opening activity showing that arginine fingers make an important contribution to the ATP-induced conformational changes that allow the clamp loader to pry open the clamp. The E. coli clamp loader can actively pry open the beta-sliding clamp.,Paschall CO, Thompson JA, Marzahn MR, Chiraniya A, Hayner JN, O'Donnell M, Robbins AH, McKenna R, Bloom LB J Biol Chem. 2011 Oct 4. PMID:21971175[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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