title: Mechanism of polymerase collision release from sliding clamps on the lagging strand.
abstract: Replicative polymerases are tethered to DNA by sliding clamps for processive DNA synthesis. Despite attachment to a sliding clamp, the polymerase on the lagging strand must cycle on and off DNA for each Okazaki fragment. In the 'collision release' model, the lagging strand polymerase collides with the 5' terminus of an earlier completed fragment, which triggers it to release from DNA and from the clamp. This report examines the mechanism of collision release by the Escherichia coli Pol III polymerase. We find that collision with a 5' terminus does not trigger polymerase release. Instead, the loss of ssDNA on filling in a fragment triggers polymerase to release from the clamp and DNA. Two ssDNA-binding elements are involved, the tau subunit of the clamp loader complex and an OB domain within the DNA polymerase itself. The tau subunit acts as a switch to enhance polymerase binding at a primed site but not at a nick. The OB domain acts as a sensor that regulates the affinity of Pol III to the clamp in the presence of ssDNA.
authors.affiliation: DNA Replication, Howard Hughes Medical Institute, The Rockefeller University, New York, NY 10021, USA.
authors.forename: Roxana E
authors.initials: RE
authors.lastname: Georgescu
authors.forename: Isabel
authors.initials: I
authors.lastname: Kurth
authors.forename: Nina Y
authors.initials: NY
authors.lastname: Yao
authors.forename: Jelena
authors.initials: J
authors.lastname: Stewart
authors.forename: Olga
authors.initials: O
authors.lastname: Yurieva
authors.forename: Mike
authors.initials: M
authors.lastname: O'Donnell
mesh_terms: D001665:Binding Sites; D004258:DNA Polymerase III / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D009154:Mutation; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D017434:Protein Structure, Tertiary
chemical_list: D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D004258:DNA Polymerase III
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