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The orderly progression of the cell cycle depends on the activation of Cdk protein by binding to its cyclin partner. However, the cell cycle must be restricted when undergoing abnormal changes. Most cancers correlate to the deregulated cell cycle, and since Cdks are a central component of the cell cycle, Cdk inhibitors are extensively studied to develop anticancer agents. For instance, cyclin D associates with several Cdks, such as Cdk 4/6, to form an active complex. The cyclin D-Cdk4/6 complex...
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The cell cycle is a series of events leading to DNA duplication followed by the division of cell content to form two daughter cells. The cell cycle progresses in four stages—the cell increases in size (gap 1 or G1-phase), duplicates its DNA (synthesis or S-phase), prepares to divide (gap 2 or G2-phase), and divides (mitosis or M-phase).
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Negative Regulator Molecules01:23

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Updated: Jun 12, 2025

Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
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CDK-dependent phosphorylation regulates PNKP function in DNA replication.

Fatemeh Mashayekhi1, Elham Zeinali1, Cassandra Ganje1

  • 1Department of Oncology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada.

The Journal of Biological Chemistry
|October 12, 2024
PubMed
Summary
This summary is machine-generated.

Polynucleotide kinase-phosphatase (PNKP) is vital for DNA replication and Okazaki fragment maturation, preventing DNA breaks linked to cancer and neurodegenerative diseases.

Keywords:
CDKsDNA replicationFEN1Okazaki fragmentsPNKPgenome instability

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Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Okazaki fragment maturation (OFM) is essential for DNA replication and genome stability.
  • Dysregulation of OFM causes DNA single-strand breaks, contributing to diseases like cancer.
  • Alternative OFM pathways, including LIG3-XRCC1, are being discovered alongside the canonical FEN1-LIG1 pathway.

Purpose of the Study:

  • To investigate the role of polynucleotide kinase-phosphatase (PNKP) in DNA replication and Okazaki fragment maturation.
  • To elucidate the mechanism and regulation of PNKP in DNA replication fork dynamics.

Main Methods:

  • Functional experiments to assess PNKP's role at replication forks.
  • Co-immunoprecipitation to determine PNKP's association with PCNA.
  • Cellular depletion studies to observe replication defects.
  • In vitro kinase assays and site-directed mutagenesis to analyze PNKP phosphorylation by CDK1/2.

Main Results:

  • PNKP is enriched at DNA replication forks and interacts with PCNA.
  • PNKP depletion causes defects similar to other OFM-related proteins.
  • PNKP is phosphorylated by CDK1/2 at multiple sites, crucial for DNA replication.
  • PNKP facilitates Okazaki fragment joining.

Conclusions:

  • PNKP plays a novel and significant role in Okazaki fragment maturation.
  • PNKP's function is regulated by CDK-mediated phosphorylation.
  • PNKP contributes to maintaining genome stability through its involvement in DNA replication.