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Multi-site phosphorylation of Pho4 by the cyclin-CDK Pho80-Pho85 is semi-processive with site preference

D A Jeffery1, M Springer, D S King

  • 1Howard Hughes Medical Institute, Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, CA 94143, USA.

Journal of Molecular Biology
|March 10, 2001
PubMed

Insights

The Pho80-Pho85 cyclin-CDK complex controls transcription factor Pho4 activity by semi-processive phosphorylation. This regulation balances inactivation and nuclear export, optimizing nutrient response.

Area of Science:

  • Molecular Biology
  • Biochemistry
  • Cell Biology

Background:

  • The Pho80-Pho85 complex is a cyclin-dependent kinase (CDK) that regulates nutrient signaling pathways.
  • Transcription factor Pho4 is a key target, and its phosphorylation by Pho80-Pho85 leads to inactivation.

Purpose of the Study:

  • To elucidate the kinetic mechanism of Pho80-Pho85 phosphorylation of Pho4.
  • To understand how site-specific phosphorylation impacts Pho4 activity and localization.

Main Methods:

  • Experimental kinetic analysis of the Pho80-Pho85/Pho4 interaction.
  • Computer modeling to simulate and interpret phosphorylation dynamics.

Main Results:

  • Pho80-Pho85 phosphorylates Pho4 in a semi-processive manner, influenced by catalytic rate (kcat) and dissociation rate (koff).
  • Preferential phosphorylation of specific sites on Pho4 was observed.
  • High-affinity site phosphorylation inhibits nuclear Pho4 activity, while low-affinity site phosphorylation promotes nuclear export.

Conclusions:

  • The semi-processive and site-selective phosphorylation mechanism allows for rapid inactivation and efficient completion of Pho4 phosphorylation.
  • This regulatory strategy enables precise control of the nutrient-responsive signaling pathway.

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