A Peptide Switch Regulates DNA Polymerase Processivity

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 100; no. 25; pp. 14689 - 14694
• Main Authors: Francisco J. López de Saro, Georgescu, Roxana E., O'Donnell, Mike
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 09.12.2003; National Acad Sciences
• Subjects: Animals; Biochemistry; Biological Sciences; Cattle; Cell cycle; Cell nucleus; Chromatography, Gel; Chromosomes; Cysteine - chemistry; Deoxyribonucleic acid; DNA; DNA - chemistry; DNA - metabolism; DNA Polymerase III - chemistry; DNA-Directed DNA Polymerase - chemistry; DNA-Directed DNA Polymerase - metabolism; Dose-Response Relationship, Drug; Electrophoresis, Polyacrylamide Gel; Escherichia coli; Escherichia coli - enzymology; Escherichia coli - metabolism; Fluorescence; Gels; Kinetics; Models, Biological; Nuclear antigens; Nucleotides; Peptides; Peptides - chemistry; Protein Binding; Protein Structure, Tertiary; Proteins; Recombinant Proteins - chemistry; replicase; RNA; Spectrometry, Fluorescence; Thymus Gland - metabolism; Time Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2435454100

Chromosomal DNA polymerases are tethered to DNA by a circular sliding clamp for high processivity. However, lagging strand synthesis requires the polymerase to rapidly dissociate on finishing each Okazaki fragment. The Escherichia coli replicase contains a subunit (τ) that promotes separation of polymerase from its clamp on finishing DNA segments. This report reveals the mechanism of this process. We find that τ binds the C-terminal residues of the DNA polymerase. Surprisingly, this same C-terminal "tail" of the polymerase interacts with the β clamp, and τ competes with β for this sequence. Moreover, τ acts as a DNA sensor. On binding primed DNA, τ releases the polymerase tail, allowing polymerase to bind β for processive synthesis. But on sensing the DNA is complete (duplex), τ sequesters the polymerase tail from β, disengaging polymerase from DNA. Therefore, DNA sensing by τ switches the polymerase peptide tail on and off the clamp and coordinates the dynamic turnover of polymerase during lagging strand synthesis.