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Experimental Approaches to Study Mitochondrial Localization and Function of a Nuclear Cell Cycle Kinase, Cdk1
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Identification of major nucleolar proteins as candidate mitotic substrates of cdc2 kinase

M Peter1, J Nakagawa, M Dorée

  • 1Swiss Institute for Experimental Cancer Research (ISREC), Epalinges.

Cell
|March 9, 1990
PubMed

Insights

Researchers identified two key nucleolar proteins, nucleolin and NO38, as targets of cdc2 kinase during mitosis. This phosphorylation by cell division kinase 2 (cdc2) regulates nucleolar structure and activity.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The cdc2 kinase is a critical regulator of cell cycle progression, particularly entry into mitosis.
  • Understanding the specific physiological targets of cdc2 kinase is essential for comprehending mitotic control.

Purpose of the Study:

  • To identify and characterize the mitotic substrates of cdc2 kinase.
  • To investigate the role of cdc2 kinase in regulating nucleolar structure and function during mitosis.

Main Methods:

  • In vitro phosphorylation assays using purified starfish cdc2 kinase.
  • Analysis of protein phosphorylation sites in vivo and in vitro.
  • Identification of phosphoacceptor motifs using synthetic peptides.

Main Results:

  • Two major nucleolar proteins, nucleolin and NO38, were found to be highly phosphorylated during mitosis.
  • These proteins were phosphorylated by purified cdc2 kinase in vitro at sites consistent with in vivo mitotic phosphorylation.
  • A TPXKK motif in nucleolin was identified as a likely mitotic phosphoacceptor site, acting as both a substrate and inhibitor for cdc2 kinase.

Conclusions:

  • Nucleolin and NO38 are novel candidate substrates for cdc2 kinase.
  • Protein phosphorylation mediated by cdc2 kinase plays a significant role in controlling mitotic alterations of nucleolar structure and activity.

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