Clb6-Cdc28 Promotes Ribonucleotide Reductase Subcellular Redistribution during S Phase
Xiaorong Wu1, Xiuxiang An1, Caiguo Zhang1,2
1Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, Colorado, USA.
Molecular and Cellular Biology
|December 22, 2017
Summary
The Clb6-Cdc28 cyclin-dependent kinase complex regulates deoxyribonucleotide synthesis by controlling the nuclear export of Rnr2-Rnr4. This phosphorylation-dependent process is crucial for maintaining genome stability during S phase.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- A regulated pool of deoxyribonucleotides (dNTPs) is essential for genome integrity.
- Ribonucleotide reductase (RNR) controls the rate-limiting step of dNTP biosynthesis.
- Subcellular localization of RNR subunits (Rnr1, Rnr2-Rnr4) is a key regulatory mechanism in *Saccharomyces cerevisiae*.
Purpose of the Study:
- To investigate the mechanism controlling the S-phase-specific relocalization of Rnr2-Rnr4 from the nucleus to the cytoplasm.
- To identify the molecular players involved in Rnr2-Rnr4 redistribution during S phase.
Main Methods:
- Investigated the role of the Clb6-Cdc28 complex in Rnr2-Rnr4 localization.
- Analyzed Rnr2 phosphorylation at a consensus CDK site.
- Assessed the impact of gene deletions (*CLB6*) and mutations on Rnr2-Wtm1 interaction and hydroxyurea sensitivity.
Main Results:
- The S-phase cyclin-CDK complex Clb6-Cdc28 directly controls Rnr2-Rnr4 nuclear-cytoplasmic relocalization.
- Rnr2 is phosphorylated by Clb6-Cdc28 in S phase, disrupting its interaction with the nuclear anchor Wtm1.
- Loss of CLB6 or the CDK site leads to nuclear retention of Rnr2-Rnr4 and increased sensitivity to hydroxyurea.
Conclusions:
- Clb6-Cdc28-mediated phosphorylation of Rnr2 triggers Rnr2-Rnr4 redistribution during S phase.
- This phosphorylation event disrupts the Rnr2-Wtm1 interaction, facilitating Rnr2-Rnr4 release from the nucleus.
- Proper Rnr2-Rnr4 localization is critical for maintaining dNTP pools and genome stability.
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